:: wikimiki.org ::
|{| class="wikitable" |+ Pressure, p (lower case) !Name of unit !Symbol !Definition !Relation to SI units |----- | pascal (SI unit) || Pa | ≡ N/m² | = kg/m·s² |----- | barye (cgs unit) || | ≡ 1 dyn/cm² | = 0.1 Pa |----- | poundal per square foot || pdl/sq ft | ≡ 1 pdl/sq ft | ≈ 1.488 164 Pa |----- | millimetre of water (3.98 °C) || mmH₂O | ≈ 999.972 kg/m³ × 1 mm × g | = 9.806 38 Pa (= 0.999972 kgf/m²) |----- | pound per square foot || psf | ≡ 1 lb/sq ft × g | ≈ 47.880 259 Pa |----- | centimetre of water (3.98 °C) || cmH₂O | ≈ 999.972 kg/m³ × 1 cm × g | = 98.0638 Pa |----- | torr || torr | ≡ 101 325/760 Pa | ≈ 133.322 368 4 Pa |----- | millimetre of mercury || mmHg | ≡ 13 595.1 kg/m³ × 1 mm × g ≈ 1 torr | = 133.322 387 415 Pa |----- | inch of water (3.98 °C) || inH₂O | ≈ 999.972 kg/m³ × 1 in × g | = 249.082 Pa |----- | pièze (mts unit) || pz | ≡ 1000 kg/m·s² | = 1 kPa |----- | centimetre of mercury || cmHg | ≡ 13 595.1 kg/m³ × 1 cm × g | = 1.333 223 874 15 kPa |----- | foot of water (3.98 °C) || ftH₂O | ≈ 999.972 kg/m³ × 1 ft × g | = 2.988 98 kPa |----- | inch of mercury || inHg | ≡ 13 595.1 kg/m³ × 1 in × g | = 3.386 388 640 341 kPa |----- | pound per square inch || psi | ≡ 1 lb × g / 1 sq in | ≈ 6.894 757×10³ Pa |----- | foot of mercury || ftHg | ≡ 13 595.1 kg/m³ × 1 ft × g | = 40.636 663 684 091 9 kPa |----- | short ton per square foot || | ≡ 1 sh tn × g / 1 sq ft | ≈ 95.760 518 kPa |----- | atmosphere (technical) || atm | ≡ 1 kgf/cm² | = 98.0665 kPa |----- | bar || bar | | ≡ 10⁵ Pa |----- | atmosphere (standard) || atm | | ≡ 101 325 Pa |----- | kip per square inch || ksi | ≡ 1 kipf/sq in | ≈ 6.894757 MPa |----- | kilogram-force per square millimetre || kgf/mm² | ≡ 1 kgf/mm² | = 9.806 65 MPa |{| class="wikitable" |+ Energy, E, W !Name of unit !Symbol !Definition !Relation to SI units |----- | joule (SI unit) || J | ≡ N·m = W·s = V·A·s | = kg·m²/s² |----- | electronvolt || eV | ≡ e × 1 V | ≈ 1.602 176×10^-19 J |----- | rydberg || Ry | ≡ R_∞·ℎ·c | ≈ 2.179 872×10^-18 J |----- | hartree || E_h | ≡ m_e·α²·c² (= 2 Ry) | ≈ 4.359 744×10^-18 J |----- | atomic unit of energy || au | ≡ E_h ≈ 4.359 744×10^-18 J |----- | erg (cgs unit) || erg | ≡ 1 g·cm²/s² | = 10^-7 J |----- | foot-poundal || ft pdl | ≡ 1 lb·ft²/s² | = 4.214 011 009 380 48×10^-2 J |----- | cubic centimetre of

Tonne

Tonne

:For the units of mass, force, and other quantities in general, see Ton. A tonne (symbol t), sometimes referred to as a metric tonne, is an measurement of weight, used in SI. Though the spelling tonne predates the introduction of the SI system in 1960 it is now used as the standard spelling for the metric weight measurement in English. The similar English units are spelt ton in English.

Definition

1 t = 1000 kg

Multiples

Origin

The spelling tonne is from French. In old English the spelling was tunne. The various spellings and meanings (tonne, ton, tun) derive from late latin tunna (cask). It may be of celtic origin. A full cask about a metre high could easily weigh 1 tonne.

Conversions

One tonne is equivalent to:
- 1 megagram (exactly). Symbol Mg. This is the SI term
- 2204.62262 pounds

Explanation

The official symbol is t, but T and mT and mt (especially in the combination mmt for "million metric tons") are also used. In France and the English-speaking countries that are predominately metric, the spelling tonne is widespread. However, in Britain, the common people consider that its measure is very close to that of the long ton and often don't bother with the distinctive spelling; for example, even the Guiness Book of World Records accepts metrification without marking this by changing the spelling. For the United States, metric ton is the name for this unit used and recommended by NIST. [http://physics.nist.gov/Pubs/SP811/sec05.html#5.1.1] In the US an unqualified mention of a "ton" almost invariably refers to a short ton. Like grams and kilograms, tonnes have also given rise to a force unit of the same name: 1 tonne-force = 9.80665 kilonewtons (kN), a unit also often called simply "tonne" or "metric ton" without identifying it as a unit of force. Note that it is only the tonne as a unit of mass which is accepted for use with SI; the tonne-force or metric ton-force is not acceptable for use with SI. The ton of TNT or tonne of trinitrotoluene is a unit of energy with the tonne as a proxy term. This unit is not acceptable for use with SI. Assuming 1000 small (thermochemical) calories per gram (4.184 kJ/g) and thus a tonne of TNT is 4.184 GJ.

References

- NIST Special Publication 811, [http://physics.nist.gov/Pubs/SP811/ Guide for the Use of the International System of Units (SI)] Category:Units of mass ko:톤 ja:トン

Ton

The word ton or tonne is derived from the Old English tunne, and ultimately from the Old French tonne, and referred originally to a large cask with a capacity of 252 wine gallons, which holds approximately 2100 pounds of water. Such a barrel (of any similar volume) is still called a tun in British English, but this usage is dying out. The modern spelling tonne, almost always referring to the metric ton of 1000 kilograms (or the associated obsolete force unit) when used in English, is a direct borrowing from the French language. There are many meanings of ton:

Units of mass

There are three similar units of mass called the ton or tonne:
- tonne or metric ton = 1000 kg (~2204.62 lb). The official symbol is t, but mT, MT, and T are also used. This is not an SI unit, though it is acceptable for use with SI. The name for this unit in SI is the megagram (symbol: Mg).
- short ton (or simply ton in the USA) = 2000 lb (exactly 907.18474 kg).
- long ton (or weight ton or gross ton, or simply ton in the UK) = 2240 lb (exactly 1016.0469088 kg), is an avoirdupois unit commonly used in the UK and still common in areas of British influence. The UK now often uses the metric (1000 kg) tonne which it is conveniently very similar to—less than 2% difference. The long ton is used for petroleum products. It is also used in the U.S., as in many other countries, for things such as the deadweight tonnage of naval ships.
- As a displacement ton the long ton is normally measured as the mass of 35 cubic feet of sea water. Increasingly, metric tons are being used rather than long tons in measuring the displacement of ships. See tonnage.
- Deadweight ton (abbreviation 'dwt') for the capacity of a ship in the number of long tons (2240 pounds).
- Harbour ton used in South Africa in the 20th century, equal to 2000 pounds or one short ton. Both the short ton and the long ton are composed of twenty hundredweights, each having different values for the hundredweight (100 and 112 pounds respectively). Prior to the 15th century in England, the ton was composed of twenty hundredweights, each of 108 lb, giving a ton of 2160 pounds. In the context of nuclear power plants, tHM and MTHM mean (metric) tons of heavy metal, and MTU means metric tons of uranium. Assay ton (abbreviation 'AT') is not a unit of measurement (nobody ever has x assay tons of something), but rather a standard quantity used in assaying ores of precious metals; it is 29 1/6 grams (short assay ton) or 32 2/3 grams (long assay ton), the amount which bears the same ratio to a milligram as a short/long ton bears to a troy ounce. In other words, the number of milligrams of a particular metal found in a sample of this size gives the number of troy ounces contained in a short/long ton of ore.

Units of force

There are also the units of force based on each of these three mass units. However, it is only the metric ton or tonne as a unit of mass which is acceptable for use with SI. The metric tonne force (tonne force), like the kilogram force, is not acceptable for use with SI.
- 1 short ton force = 2000 lbf = 8.896443230521 kilonewtons (kN)
- 1 long ton force = 2240 lbf = 9.96401641818352 kN
- 1 metric ton force = 1000 kgf = 9.80665 kN

Units of volume

See also ton (volume), tonnage. The freight ton or measurement ton is a unit of volume used for describing ship capacities (tonnage) or cargo. One measurement ton is equal to:
- 40 cubic feet
- 1.481(481) cubic yards (the "481" digit sequence repeats infinitely)
- 1,132.67386368 litres
- 1.13267386368 cubic metres The amount of fresh water at 4 °C displaced by one measurement ton has a mass similar to the ton masses listed above: about 1133 kg or 2497 lb. The measurement ton is abbreviated as M/T, MT, or MTON, which can cause it to be confused with the metric ton. The register ton is also a unit of volume used for the cargo capacity of a ship, defined as 100 cubic feet (roughly 2.83 cubic metres). It is often abbreviated GRT for gross registered ton. It is known as a tonneau de mer in Belgium, but, in France, a tonneau de mer is 1.44 cubic metres or about 1.88 cubic yards. The Panama Canal net ton, a unit of volume used for billing for ships going through the Panama Canal, the same as the register ton. The fee for example in the 1990s was roughly a couple USD for each unit. The water ton was formerly used in Great Britain and equal to 224 imperial gallons (the volume occupied by a mass of one long ton under the conditions which define the imperial gallon). See 1 E-1 m³ and orders of magnitude (volume) for a comparison with other volumes.

Unit of energy

ton of TNT

- A ton of TNT or tonne of TNT is a unit of energy equal to 10⁹ calories, also known as a gigacalorie, equal to about 4.184 gigajoules.
- A kiloton of TNT or kilotonne of TNT is a unit of energy equal to 10¹² calories, also known as a teracalorie, equal to about 4.184 terajoules.
- A megaton of TNT or megatonne of TNT is a unit of energy equal to 10¹⁵ calories, also known (infrequently) as a petacalorie, equal to about 4.184 petajoules. Note that these are thermal calories. The dietary calorie is equal to one thousand thermal calories. Early values for the explosive energy released by trinitrotoluene (TNT) ranged from 900 to 1100 calories per gram. In order to standardise the use of the term TNT as a unit of energy, an arbitrary value was assigned based on 1000 calories (4.184 kilojoules) per gram. Thus there is no longer a direct connection to the chemical TNT itself. It is now merely a unit of energy that happens to be expressed using words normally associated with mass (e.g. kilogram, tonne, pound) (IAEA references: [http://www.iaea.org/About/Policy/GC/GC42/Documents/gc42inf3.pdf], [http://www.iaea.org/Publications/Magazines/Bulletin/Bull404/article1.pdf]). The definition applies for both spellings: ton of TNT and tonne of TNT. Measurements in tons of TNT have been used primarily to express nuclear weapon yields, though have also been used since in seismology as well. Sample terms:

ton of coal equivalent

- A ton of coal equivalent or tonne of coal equivalent (TCE), a conventional value of 7 Gcal (IT) = 29.3076 GJ.

ton of oil equivalent

- A ton of oil equivalent or tonne of oil equivalent (TOE), a conventional value of 10 Gcal (IT) = 41.868 GJ ≈ 10.0067 ton of TNT. See also GTOE.

Unit of power

- In refrigeration and air-conditioning, a refrigeration ton can be:
- The power required to cool 1 short ton of water by 1 °F every 10 minutes = 12,000 BTU/h ≈ 3,516.85284 watts
- The power required to cool 1 long ton of water by 1 °F every 10 minutes = 13,440 BTU/h ≈ 3,938.87518 watts
- A corresponding unit of energy equal to that power for a period of a day, or 24 × 12,000 BTU = 288,000 BTU ≈ 303,856,086 joules

Miscellaneous tons

- Ton is also used informally to mean a large amount of something.
- Units of speed: in slang or informal usage, a ton can be
- 100 mph
- 100 km/h
- In money, a ton is slang for 100 GBP (pounds sterling) —this is a term with a London, England origin.
- In darts, a ton (or ton up) is a score of 100 or more points with three darts.
- In cricket, a ton is a score of 100 runs, typically referring to 100 runs by a single batsman.
- In motor vehicles, many trucks are classified into groups loosely related to their off-road carrying capacity, as 1/4-ton (the first Jeep was so classified), 1/2-ton, 3/4-ton, 2 1/2-ton (deuce-and-a-half in U.S. military slang), 5-ton, etc. Of course, the vehicles weigh much more than this, and according to military classification are allowed to carry double the cargo on roads.
- Conversely in some cases the weight refers to the maximum gross road weight including cargo, for example a British 3.5-tonne van is the largest vehicle that can be legally driven on an ordinary driver's license.

External links

- [http://www.ex.ac.uk/trol/scol/ccvol.htm Conversion calculator for units of mass (Cleave Books)] Category:Units of mass Category:Units of volume Category:Customary units in the United States Category:Imperial units ko:톤 ja:トン simple:ton

English unit

The term English units refers to one of a number of systems of units of measurement, some obsolete, and some still in use. In spite of the name, it does not necessarily refer to the (non-SI) system of units still in intermittent use in England itself. In fact, the latter is often referred to outside the United States as the Imperial System. Various different standards under the name 'English units' have applied at different times, in different places and for different things. Prior to the Battle of Hastings in 1066 the Anglo-Saxon system of measurement had been based on the units of the barleycorn and the gyrd (rod). This system presumably had Germanic origins. After the Norman conquest Roman units were reintroduced. The resultant system of English units was a combination of the Anglo-Saxon and Roman systems. Later development of the English system continued by defining the units by law in the Magna Carta of 1215, and issuing measurement standards from the then capital Winchester. Standards were renewed in 1496, 1588 and 1758. The last Imperial Standard Yard in bronze was made in 1845; it served as the standard in the United Kingdom until the yard was internationally redefined as 0.9144 metre in 1959 (statutory implementation: Weights and Measures Act of 1963). The use of English units spread throughout the British Isles and to the British colonies. These units form the basis for the Imperial system formerly used in Commonwealth countries and U.S. customary system used in the United States of America. Whilst these two systems are quite similar there are a number of notable differences between the Imperial and U.S. systems.

Historical English units

Length

; poppyseed : ¼ of a barleycorn ; barleycorn : Basic Anglo-Saxon unit, the length of a corn of barley. The unit survived after 1066, redefined as 1/3 inch. Note the relation to the grain unit of weight. ; digit : ¾ inch ; finger : 7/8 inch ; ynch, inch : Anglo Saxon inch, 3 barleycorns. Based on the Roman uncia from 1066. ; nail : 3 digits = 2¼ inches = 1/16 yard ; palm : 3 inches ; hand : 4 inches ; shaftment : Width of the hand and outstretched thumb, 6½ ynches before 1066, 6 inches thereafter ; span : Width of the outstretched hand, from the tip of the thumb to the tip of the little finger, 3 palms = 9 inches ; foot : Usually 13 ynches but also other variants. Shortened by basing it on the Roman pes from 1066. ; cubit : Forearm, 18 inches ; yard : Introduced after 1066, 3 feet = 36 inches. ; ell : Elbow, 20 nails = 1¼ yard or 45 inches. Mostly for measuring clothing ; fathom : From one fingertip to the other, 6 feet ; rod : Saxon gyrd measuring stick, might have been from 20 "natural feet". Retained its length but redefined as 16 ½ Roman feet after 1066. ; furlong : "Furrow long" (Saxon furrow is furh), probably based on the ancient Mediterranean stadion, defined as 40 rods ; mile : Introduced after 1066, originally the Roman mile at 5000 feet, in 1592 it was extended to 5280 feet to make it an even number of furlongs, i.e. 8. ; league : Usually three miles. Intended to be an hour's walk. ; chain : Any of several actual chains used for land surveying and divided in links. Gunter's chain, introduced in the 17th century, is 66 feet.

Area

; acre : Saxon unit, meaning "field", one furlong by 4 rods. Probably meant to be "as much area as could be plowed in one day".

Volume

General

In both Britain and America, in addition to perch as a measure of length, there is also the perch which refers to the volume measurement of stone; one perch is equal to 16.5 ft × 1.5 ft × 1 ft = 24.75 cu. ft. of dry stone. The relationship to the unit of length (one perch = 16.5 feet) should be obvious.

Wine

Brewery

Weight

The Avoirdupois, Troy and Apothecary systems of weights all shared the same finest unit, the grain, however they differ as to the number of grains there are in a dram, ounce and pound. Originally, this grain was the weight of a grain seed from the middle of an ear of barley. There also was a smaller wheat grain, said to be ¾ (barley) grains or about 48.6 milligrams.

Avoirdupois

; grain (gr) : ≈ 65 mg ; dram/drachm (dr) : 27.34375 gr (sixteenth of an ounce) (possibly originated as the weight of silver in ancient greek coin drachma) ; ounce (oz) : 16 dr = 437.5 grains ≈ 28 g ; pound (lb) : 16 oz = 7000 grains ≈ 454 g ; quarter : ¼ cwt ; hundredweight (cwt) : 112 lb (long) or 100 lb (short) ; ton : 20 cwt Additions: ; nail : 1/16 cwt = 7 lb ; clove : 7 lb (wool) ; stone (st) : 2 cloves = 14 lb (an Anglo-Saxon unit changed to fit in) ; tod : 2 st = ¼ cwt (long)

Troy

; grain (gr) : ≈ 65 mg ; pennyweight (dwt) : 24 gr ≈ 1.56 g ; ounce (oz t) : 20 dwt = 480 gr ≈ 31.1 g ; pound (lb t) : 12 oz t = 5760 gr ≈ 373 g ; mark: 8 oz t

Tower

; tower ounce : 18¾ dwt = 450 gr ≈ 29 g ; tower pound : 12 oz T = 225 dwt = 5400 gr ≈ 350 g The Troy and Tower pounds and their subdivisions were used for coins and precious metals. The Tower pound, which is based upon an earlier Anglo-Saxon pound, was abolished in 1527. In terms of (silver) currency a pound was 20 shillings of 12 pennies each (i.e. 240) from the late 8th century (Charlemagne/Offa of Mercia) to 1971 in Great Britain, but lighter than a troy one.

Apothecary

; grain (gr) : ≈ 65 mg ; scruple (s ap) : 20 gr ; dram (dr ap) : 3 s ap = 60 gr ; ounce (oz ap) : 8 dr ap = 480 gr ; pound (lb ap) : 5760 gr = 1 lb t

Others

; Merchants/Mercantile pound : 15 oz tower = 6750 gr ≈ 437.4 g ; London/Mercantile pound : 15 oz troy = 16 oz tower = 7200 gr ≈ 466.6 g ; Mercantile stone : 12 lb L ≈ 5.6 kg ; Tron pound (Edinburgh/Scots) : 16 oz Tron ≈ 623.5 g ; Butcher's stone : 8 lb ≈ 3,63 kg ; Sack : 26 st = 364 lb ≈ 165 kg The carat was once specified as four grains in the English-speaking world. Some local units in the English dominion were (re-)defined in simple terms of English units, such as the Indian tola of 180 grains. See also: slug and poundal.

External links

- [http://www.unc.edu/~rowlett/units/custom.html English Customary Weights and Measures]
- Jacques J. Proot's [http://users.aol.com/jackproot/met/spvolas.html Anglo-Saxon weights & measures] page. Category:Systems of units Category:Units of length Category:Units of area Category:Units of volume Category:Units of mass Category:Imperial units Category:Customary units in the United States

Guiness Book of World Records

Guinness Book of Records

Metrification

s on a car showing the speed of the vehicle in miles and kilometres per hour.]] Metrication or metrification is the process of converting from the various other systems of units used throughout the world to the SI metric system. This process began in France in the 1790s and spread over the following two centuries to all but four countries, representing 95% of the world's population. The process was completed in most of the world in the 19th and early 20th centuries, replacing numerous historical weights and measures. The countries of the former British Empire (with the exception of the United States) completed metrication during the second half of the 20th century, with the Republic of Ireland recently completing metrication on January 20 2005. Today only the United States, Liberia, and Myanmar have not officially switched to the metric system (although Liberia and Myanmar use it in practice) and the United Kingdom is currently in the process of conversion. Only France, the United States, the United Kingdom, and Japan have seen significant popular opposition to metrication, the main objections being based on tradition, aesthetics, economical impact and distaste for measures viewed as foreign.

Before the metric system

Medieval trade was organized on a city-by-city basis by guilds, which set local laws on weights and measures. For example, the ell or elle was a unit of length commonly used in Europe, but its value varied from 40.2 cm in one part of Germany to 70 cm in The Netherlands to 94.5 cm in Edinburgh. A survey of Switzerland in 1838 revealed that the foot had 37 different regional variations, the ell had 68, there were 83 different measures for dry grain and 70 for fluids, and 63 different measures for "dead weights."^[2] When Isaac Newton wrote his important work Philosophiae Naturalis Principia Mathematica in 1687, he quoted his measurements in Parisian feet so his readers could understand their size. Various efforts were made to have local intercity or national standards for measurements, such as a Scottish law of 1641 and the British standard Imperial unit system of 1845, which is still used for some things in the UK. However, revolutionary France was to produce the definitive International System of Units which has come to be used by most of the world today. The desire for a single international system of measurement derives from growing international trade and the need to apply common standards to goods. For a company to buy a product produced in another country, they need to be sure that the product will arrive as described. The medieval ell was abandoned in part because its value could not be standardised. It can be argued that the Système International's (SI) primary advantage is simply that it is international, and the pressure on countries to conform to it grew as it became increasingly an international standard. SI is not the only example of international standardisation; several powerful international standardisation organisations exist for various industries, such as the International Organization for Standardization, the International Electrotechnical Commission, and the International Telecommunication Union. Indeed, writing is probably the only area of modern life which has not been standardised internationally, there being hundreds of alphabets in current use. For example, there are 28 variations of the Latin alphabet and Japanese alone uses four different alphabets, a situation analogous to measurement before metrication. An International Phonetic Alphabet exists that can efficiently represent all vocal sounds, however it is commonly used only by linguists.

Système International (SI)

:See main article: International System of Units Scientists, chiefly in France, had been advocating and discussing a decimal system of measurement based on natural units at least since 1640, but the first official adoption of such a system was after the French Revolution of 1789. The creators of the metric system tried to choose units that were non-arbitrary and practical, merging well with the revolution's official ideology of "pure reason". The original system started with the metre as the unit of distance, the gram as the unit of mass, and the second as the unit of time. Derived units are made from logical combinations of base units. For example, the speed of an object is defined by the number of metres it moves every second — m/s. An object that is accelerating has a changing speed, so its m/s changes per second, thus the unit is m/s². The force exerted on an object can be described by its mass times the resulting acceleration of the object, thus—kg·m/s²—which is the newton (symbol N), named in honour of Isaac Newton. Further base units dealing with electricity, light and quantities of atoms were added later as these sciences became better understood. The current version of this system was agreed upon in 1971 and is organised and maintained by the International Bureau of Weights and Measures. To avoid confusion over the precise value of base units, this organisation also maintains either an international prototype (in the case of a kilogram, a small object of platinum-iridium dubbed "Le Grand Kilo") or a precise recipe on how to recreate the unit, which is decided by the General Conference on Weights and Measures held every four years. Time has resisted metrication. During the French revolution there was an attempt at a decimal time system with 100 seconds in a minute, 100 minutes in an hour and 10 hours in a day (100,000 seconds in a day as opposed to 86,400 currently—a metric second would be thus 14% shorter). The proposed system also included a ten-day week, which was probably its main reason for failure. The church and the people objected and the system was dropped. It is also interesting to note that the Chinese calendar had an almost identical decimal time system up until the 17th century.[http://www.decimaltime.hynes.net/history.html]

Conversion process

There are three common routes that nations take in converting from traditional measurement systems to the metric system. The first is a quick, so called "Big-bang" route which was used by India in the early 1960s and several other developing nations since then. The second two routes are both variations on the slower phase-in route that tends to be favoured by industrial nations. The first, "Big-bang", route is to simultaneously outlaw the use of pre-metric measurement, metricise and reissue all government publications and laws, and change education systems to metric. India's changeover lasted from 1 April 1960, when metric became legal, to 1 April 1962, when all other systems were banned. The Indian model was extremely successful and was copied over much of the developing world. The second possibility, and first phase-in route, is to pass a law permitting the use of metric units in parallel with traditional ones, followed by progressively banning the use of the older measures. This has generally been a slow route to metric. The British Empire permitted the use of metric in 1873, but the changeover was not completed until the 1970s and 1980s when government took an active role in the now-independent parts of the empire. Japan, too, followed this route and did not complete the changeover for 70 years. A final possibility is to redefine traditional units in terms of metric values. These redefined units often stay in use long after metrication is said to have been completed. China followed this route, and thus while scientists in China know and use the kilogram, common people retain the jin, which now has a value of 500 g. (This route was once proposed for England with the pound to be redefined as 500 g, but the plan did not receive government support.) In the Netherlands, 500 g is informally referred to as a pond (pound) and 100 g as an ons (ounce), and in Germany and France 500 g is informally referred to respectively as ein Pfund and une livre (one pound). In Denmark, the re-defined pund (500 g) is occasionally used, particularly among older people and (older) fruit growers, since these were originally paid according to the number of pounds of fruit produced. It is difficult to judge the degree to which ordinary people change to using metric in their daily lives. In countries that have recently changed, older segments of the population tend to still use the old, and more familiar to them, system. Also, local variations abound in what exactly becomes metricated and what does not. In Canada, for example, ovens and cooking temperatures are usually measured in Fahrenheit, and Canadians almost invariably use Fahrenheit for cooking; though this is not necessarily by choice but may instead be due to the overwhelming influence of the neighbouring and largely non-metricated United States. In the UK, which is still in the process of changing over, metric units are often used interchangeably with older measurements. Such countries could be said to be "semi-metric".

Adoption

UK The metric system, developed in France around the turn of the 19th century, was quickly taken up by Europe's scientists before spreading to traders and industrialists and finally to the common people. France's neighbour the Kingdom of the Netherlands (present The Netherlands, Belgium, and Luxembourg), changed in 1820. Spain and its former American colonies changed in the 1850s and 1860s. Italy and Germany went metric after their respective unifications in 1861 and 1871, followed shortly by Portugal, Norway, Sweden and Austria-Hungary. By 1900, 39 countries in Europe and Latin America were using the metric system. The first Asian nations to convert were Mongolia (1918), Cambodia and Afghanistan (the 1920s). Japan began its slow conversion process in 1891 when it received a copy of the metre standard from the Institute in France. In 1924, the government decided to replace fully the traditional shaku-kan system within 10 years; however, public opposition delayed implementation. The U.S. occupation of the late 1940s briefly caused a de facto conversion to U.S. customary units. Metrication was completed in Japan by 1969, although some of the old units are still in informal use. India's conversion was far quicker, paradoxically helped by low popular literacy and the fact that there was previously no nationwide standard measurement system—British Imperial units were used by the upper class, while various regional systems were used by the poor. From 1956 to 1961, India simultaneously changed to metric and decimalised its currency. China began conversion in the 1920s, but the process was not completed until communist times. China also decimalised their native measurement units and redefined them as even amounts of metric units. Thus jin was redefined to equal 500 grams. The Soviet Union changed from traditional units to metric in 1924. Those Arab nations which were colonized by France adopted the system early: Algeria changed in 1840, Tunisia in 1890; this was extended to the other Arab countries after the conquest of the Ottoman Empire in 1918. Jordan, which had been a British mandate, was the last Arab nation to convert, in the 1950s. The German colonies of Rwanda and Burundi and the Belgian Congo (now Democratic Republic of Congo) were the first sub-Saharan African states to go metric in 1910. French territories in Africa were de facto metric while under French rule. On independence all gradually passed official metric weights and measures laws during the 1950s and 1960s. The last African states to go metric were the former British colonies of southern and eastern Africa. Democratic Republic of Congo Britain and its former colonies (with the notable exception of the United States) began their conversion process in the later part of the 20th century. South Africa began a ten-year process of metrication in 1967 with the creation of Metrication Advisory Board, a Metrication Department and a South African Bureau of Standards. Australia began work in 1969 with a publicity campaign involving lecture tours, theatrical advertisements and the free distribution of metric-sized items, including calendars, rulers and A4-sized leaflets. Public opposition was on points of detail only, and the process was declared completed in 1977. Canada and New Zealand followed similar plans in the 1970s. Ireland completed a very gradual changeover process on 20 January 2005 with the conversion of road speed limits to km/h. Ireland began metrication in 1970 when schools switched to teaching only the metric system.

Exceptions

There are three main exceptions to the metrication trend: the UK, the U.S., and global air and sea transport industry. Contrary to popular belief, the U.S. and the UK do not use a common system (see English unit, Imperial unit and U.S. customary units for details). With the exception of the length, with the yard standardised at exactly 0.9144 m by an international conference in 1958, most other units differ in value in the U.S. and UK. A gallon of liquid, for example, is 3.8 l in the U.S. but 4.5 l in the UK. The U.S. also has a dry gallon, which is 4.4 l.

United Kingdom

gallon :See also: Metrication in the UK The UK made initial moves to convert to metric as long ago as 1862, when the Select Committee on Weights and Measures favoured the introduction of metric weights and measures accompanied by decimalisation of the currency.[http://www.dti.gov.uk/ccp/topics1/pdf1/met1862.pdf] The country finally decimalised their currency over a century later in 1971. There is some public resistance to metrication, which some see as the imposition of a foreign system and to be connected with other unpopular ideas from mainland Europe, such as the Euro. The "metric martyrs" were shop owners in the UK who were fined for refusing to use metric units and for overcharging in response to metric customer requests. metric martyrs The result has been a mixture of metric and non-metric units, although metric units have gradually been phased in. Metric units have been taught in UK schools since the late 1960s, and certain industries also converted or largely converted decades ago. For example, the paper industry converted in 1970 and the construction industry between 1969 and 1972—although certain products continue to be produced to imperial sizes but with metric size descriptions, for example, as 13 mm (rather than as half-inch) thick plasterboard. However, draught beer and cider are still sold in pints, milk may be sold in pints in returnable containers, and the mile, yard, foot and inch are used for road signage and associated measurements. The acre is used for land registration (although any registration since 1995 has used metric measurements). These units are defined in terms of SI units. Other exceptions include aviation, shipping and rail transport. For example, the foot for aircraft altitude, nautical miles and knots ([http://www.opsi.gov.uk/si/si1995/Uksi_19951804_en_1.htm], [http://europa.eu.int/eur-lex/lex/LexUriServ/site/en/consleg/1980/L/01980L0181-19791221-en.pdf]). In August 2005, the European Commission announced it would require Britain to set a legal deadline for the completion of metrication.[http://www.guardian.co.uk/eu/story/0,7369,1558081,00.html]

United States

European Commission :See also: Metrication in the United States and Fair Packaging and Labeling Act The United States remains the main exception. Although Thomas Jefferson recommended metrication and currency decimalisation, and metrication has been the official policy of the U.S. government since the Convention du Mètre (Metre Convention), and several laws encourage or require use of metric units in various contexts [http://lamar.colostate.edu/~hillger/laws/index.html], the progress of metrication has been much slower in the United States than in the rest of the world. Non-metric units continue to be predominantly used in everyday life and in commerce, engineering, and aviation, although most scientific work in the U.S. is now conducted using metric units. However, change has occurred, with most products in the U.S. now required by law to be labeled with both metric and non-metric units, and a number of companies and government agencies switching to metric standards. Additionally, the metric system is taught in schools, in the context of the sciences. One peculiar example of this is bottled soft drinks, commonly sold in units of two litres, and with units of 500 ml, one litre, and three litres being less, but increasingly, common. This is a result of the introduction of PET bottling technology coinciding with a particularly strong metrication push in the mid to late 1970s; consumers found that they could buy a two-liter plastic bottle of their favorite soft drink more cheaply than they could four one-pint glass bottles, and the convention stuck. Smaller units, however, continue to be sold more often in fluid ounces, such as 8 ounce (240 ml) and 12 ounce (355 ml) aluminium cans and 20 ounce (591 ml) PET bottles. Some other products, notably toiletries such as shampoo and mouthwash, have begun to be sold in metric sizes, and PowerBars and similar products have always been sold in metric sizes. The United States continues to use only miles for road distance signs, with the exception of Interstate 19 in Arizona, some roads in Hawaii and a stretch of the westbound New York State Thruway between I-81 and I-481 near Syracuse. Delaware Route 1 in Delaware between Dover Air Force Base and Interstate 95 uses a dual-measurement system in which distances are in miles but exit numbers are based on the kilometric distances from the road's beginning. Some states have experimented with dual-unit signs, particularly near the borders with Canada and Mexico, but there are as yet no plans for large-scale conversion. Originally, U.S. legislation set October 2000 as a deadline by which states must undertake construction work and statistics in metric for states to be eligible for federal funding, but that requirement has since been rescinded. There is presently little political or popular support for a comprehensive switch to the metric system.

Liberia and Myanmar

Liberia has used the U.S. system of weights and measures since its founding in the 19th century by freed slaves from the United States. In modern times instability and civil war has meant that measurement reform has not been a high priority and the country in fact uses a mixture of U.S., metric and local customary measures. Myanmar has not officially adopted "everyday use" of the metric system, but unofficial metrication has taken place and the Myanmar economy primarily operates using the metric system.

Air and sea transport

Some industries have resisted metrication. Non-metric measures in air and sea transport retain worldwide dominance. In these areas the nautical mile (1.852 km) is preferred over the kilometre, because it closely represents a minute of arc of the circumference of Earth. While the metre was also based on the Earth with 100 km equal to an arc of 1 grad, those units of angle have not seen widespread use, though they do appear on some maps. The knot, which is nautical miles per hour, remains the prime unit of speed for maritime and air navigation. (However, before the 1960s, statute miles per hour—which bear no relationship to the Earth—were most often used for this purpose, and remained in fairly common use for some purposes into the 1970s and later.) For aviation, altitudes are usually estimated based on air pressure values and described in nominal feet rather than nominal metres. However, several countries and air forces (mainly, but not only former Warsaw Pact) use metres for altitude. Thus an individual pilot can sometimes operate with altitudes in metres and sometimes in feet. The policies of the International Civil Aviation Organization (ICAO) relating to measurement are:
- there should be a single system of units throughout the world
- the single system should be SI
- the use of the foot for altitude is a permitted variation Consistent with ICAO policy, aviation has undergone a lot of metrication over the years. For example, the United Kingdom and Ireland metricated runway length and many other measures several decades ago. The United States metricated temperature reports in 1996 and the US military has metricated some reports of visual range. Metrication is also gradually taking place in cargo weights/dimensions and fuel volume/weight.

Accidents and incidents

Confusion over units during the process of metrication can sometimes lead to accidents. One of the most famous examples is the Gimli Glider, a Boeing 767 that ran out of fuel in Canada in 1983 due, in large part, to confusion at Air Canada during Canada's metrication. While not strictly an example of national metrication, the use of two different systems was the contributing factor in the loss of the Mars Climate Orbiter in 1998. NASA specified metric units in the contract. NASA and other organisations worked in metric units but one subcontractor, Lockheed Martin, provided thruster performance data to the team in pound force seconds instead of newton seconds. The spacecraft was intended to orbit Mars at about 150 km altitude but the incorrect data meant that it descended to about 57 km and probably burned up in the Martian atmosphere.

Opposition

Interestingly, considering it was the birthplace of the metric system, France experienced a particularly rough journey to metrication. The traditional French measuring system was chaotic, with size of units differing in each small town, and often even within towns. Lyon had two different values of pound in general use, one of 14 ounces, and another of 15 ounces, the latter only being used for measuring silk. The revolutionary government, which had ordered the creation of the metric system, first attempted a quick conversion, legalising metric in 1795 and, just four years later, banning the use of traditional units. Massive popular opposition led Napoleon, after he came to power, to roll back these reforms. He publicly denounced the previous government for "tormenting people with trifles". It appears that it was decimalisation that disturbed the people most — as, although Napoleon decreed that there should be "such fractions and multiples as were generally used", he redefined the old base units in metric terms. The original metric system was made law again in France in 1837.^[2] Few countries experience much popular opposition to metrication. Many, such as 19th century Europe, Russia, India and China, converted before most of their populations were literate, and so the initial conversion affected few people. For others, such as Ireland, the previous system was also seen as foreign and unloved. Japan also saw popular resistance to their 1920s metrication program, where opponents of the metric system believed that the adoption of a foreign measuring system would have a bad influence on national sentiment, cause dislocations in public life, needless expense to the nation, prove disadvantageous to foreign trade, and would hurt the national language and culture. In 1933, the government postponed the date of the first stage of conversion by five years, and the date of the second stage by ten years. The US occupation resulted in a temperary conversion to US customary units. The post-war manufacturing boom required an international standard measurement system and the issue was persued again in the 1950's and 60's. The process was not finally completed until 1969, however, traditional units are still used for measurements of sake and the area of land and appartments.

References

# # #

External links

Websites supporting metrication:
- [http://www.gometric.ie The Metrication Board of Ireland]
- [http://www.metric.org.uk/home.htm The United Kingdom Metric Association] campaigns for a total metric switchover in the UK
- [http://www.metric.org.uk/press/timeline.htm Timeline of metric system in UK]
- [http://lamar.colostate.edu/~hillger/internat.htm U.S. Metric Association] discusses progress of metrication in several countries.
- [http://members.shaw.ca/gw.peterson/metric.html One Metre: Metric in Canada] Websites opposing metrication:
- [http://www.hostess.com/womanhood/f2m Freedom to Measure] discusses the freedom to choose a measurement system
- [http://www.bwmaonline.com/ British Weights and Measures Association] Other:
- [http://calc.skyrocket.de/en/ Online Unit Converter - Conversion of many different units]
- [http://www.onlineconversion.com OnlineConversion.com] Category:Systems of units Category:History of science Category:Engineering Category:Measurement
-

Newton

---- The newton (symbol: N) is the SI unit of force. It is named after Sir Isaac Newton in recognition of his work on classical mechanics.

Definition

A newton is the amount of force required to accelerate a mass of one kilogram at a rate of one metre per second squared. :1 N = 1 kg·m·s^–2

SI multiples

Explanation

The notions of mass and force are often confused in everyday life, but must be kept separate in science and engineering. The newton was first used around 1904, but not until 1948 was it officially adopted by the General Conference on Weights and Measures (CGPM) as the name for the MKS unit of force. Rather fittingly, given the story about how Newton arrived at his theory of gravity after contemplating why an apple falls downwards, the mass of a small apple exerts a force of about 1 newton on Earth.

Conversions

Megaton

Ton#ton_of_TNT

Calorie

A calorie is a unit of measurement for energy. In most fields, it has been replaced by the joule, the SI unit of energy. However, it remains in common use for the amount of energy obtained from food. Many different definitions for the calorie have emerged during the 19th and 20th century. They fall into two classes:
- The small calorie or gram calorie is the energy needed to increase the temperature of 1 g of water by 1 °C. This unit of energy is equivalent to about 4.185 J.
- The large calorie or kilogram calorie is the energy needed to increase the temperature of 1 kg of water by 1 °C. This unit of energy is 1000-times larger than the gram calorie and equivalent to about 4.185 kJ. The kilogram calorie is today also called kilocalorie (symbol: kcal). The international standard definition of the term "calorie" (symbol: cal) refers today to the gram calorie; this way, the term kilocalorie can also be interpreted to mean 1000 calories. However, where the term "calorie" is used in nutrition and food labeling, it commonly refers to the kilocalorie.

Nutrition and food labels

nutrition The "calorie" has become a common household term, because dietitians recommend in cases of obesity to reduce body weight by increasing exercise (energy expenditure) and reducing energy intake. Many governments require food manufacturers to label the energy content of their products, to help consumers control their energy intake. In Europe, manufacturers of prepackaged food must label the nutritional energy of their products in both kilocalories ("kcal") and kilojoules ("kJ"). In the United States, the equivalent mandatory labels display only "calories" (meaning kilocalories); an additional kilojoules figure is optional. The energy content of food is is usually given on labels for 100 g and for a typical service size. The amount of food energy in a particular food could be measured by completely burning the dried food in a bomb calorimeter, a method known as direct calorimetry [http://www.merck.com/mmhe/sec12/ch152/ch152e.html]. However, the values given on food labels are not determined this way, because it overestimates the amount of energy that the human digestive system can extract, by also burning dietary fibre. Instead, standardized chemical tests and an analysis of the recipe are used to estimate the product's digestable constitutents (protein, carbohydrate, fat, etc.). These results are then converted into an equivalent energy value based on a standardized table of energy densities: Other substances found in food (water, non-digestable fibre, minerals, vitamins) do not contribute to this calculated energy density. Recommended daily energy intake values for young adults are 2500 kcal/d (10 MJ/d, 120 W) for men and 2000 kcal/d (8 MJ/d, 100 W) for women. Children, sedentary and older people require less energy, physically active people more.

Versions

Three definitions of the calorie are today recognized internationally: Other historic definitions include
- the 4 °C calorie, and
- the mean 0 °C to 100 °C calorie. Of all these, what is most commonly meant by calorie in contemporary English text is the 15 °C calorie. The nutritional (kilo)calorie equals 1000 cal₁₅. Since these many definitions are a source of confusion and error, all calories are now deprecated. The International System of Units (SI) unit for heat (and for all other forms of energy) is the joule (J), while the (obsolete) CGS system used the erg.

Trivia

- Unicode has a symbol for "cal": (㎈), but this is just a legacy code to accommodate old code pages in certain Asian languages, and it is not recommended for use in any language today.
- The conventional value chosen to define a ton of TNT is equal to 1 billion thermochemical calories: 1 t_TNT ≡ 1 × 10⁹ cal_th. The actual energy liberated from the explosion is somewhat more; see megaton.
- Nutritionists say that there are 3500 kcal (approximately 15 megajoules) of metabolizable energy in 1 lb (approximately 450 g) of fat. Therefore, to lose 1 lb of fat, one has to create a −3500 kcal deficit between intake and outgo. This works out to 7700 kcal (or 32 megajoules) per kilogram of fat.

External links

- [http://www.healthyweightforum.org/eng/calorie-counter/ Calorie Counter] Searchable calorie database of over 11,000 foods - Including fast food (website has pop-up ads)
- [http://www.nutritiondata.com/ NutritionData's Nutrition Facts Calorie Counter]
- [http://www.calorie-count.com/ Calorie Counter Database]

References

- [http://europa.eu.int/scadplus/leg/en/lvb/l21092.htm European Union regulations on nutrition labeling]
- United Kingdom [http://www.opsi.gov.uk/si/si1996/Uksi_19961499_en_1.htm Food Labelling Regulations 1996] – [http://www.opsi.gov.uk/si/si1996/Uksi_19961499_en_13.htm#sdiv7 Schedule 7: Nutrition labelling]
- United States federal food-labeling regulations [http://edocket.access.gpo.gov/cfr_2004/aprqtr/21cfr101.9.htm 21CFR101.9]
- NIST Special Publication 811, Appendix B8: [http://physics.nist.gov/Pubs/SP811/appenB8.html#C calorie].
- Donatelle, Rebecca J. Health: The Basics. 6th ed. San Francisco: Pearson Education, Inc. 2005. Category:Units of energy Category:Nutrition ko:칼로리 ja:カロリー

Ton of oil equivalent

:TOE also stands for Theory of Everything The ton of oil equivalent (TOE) is a unit for measuring energy. It corresponds to 10 Gcal_th or 41.84 GJ (41,840,000,000 joules), or 11.62 MWh. It is the rounded-off amount of energy that would be produced by burning one metric ton of crude oil. Since crude oil of different provenance will have a different chemical make-up and therefore give off varying amounts of heat when burnt, the value is conventional to a certain extent. The TOE is commonly used for large amounts of energy, since it may be easier to understand in a practical context than the proper SI unit for energy, the joule. A barrel of oil equivalent (BOE), also a unit of energy, contains approximately 0.146 TOE (i.e. there are approximately 6.841 BOE in a TOE). A GTOE (gigaton of oil equivalent) is 1,000,000,000 tons of oil equivalent. Note that some organisations use other conversion factors, such as:
- One TOE is 42 GJ
- One TOE is 7.11, 7.33, or 7.4 barrels of oil equivalent
- One ton petroleum equivalent (TPE), a parameter used in renewable energy, 10,800,000,000 cal_IT (45.217 gigajoules).

GTOE

GTOE is an abbreviation for "gigatonne of oil equivalent", a common measure of global energy. It is a billion ton of oil equivalent (TOE), hence 10,000,000,000,000,000,000 calories (as in the energy to heat one gram of water one degree Celsius, not "Calories" as in the food measurement —also known as the kilocalorie) or 41.868 EJ (exajoules) or 11.63 PW·h (petawatt-hours). As of 2003, the world uses roughly 9 GTOE (380 EJ) worth of energy per year, from all energy sources combined with an annual growth rate of roughly 3%.

Ton

Units of mass

Units of force

Units of volume

Unit of energy

ton of TNT

ton of coal equivalent

- A ton of coal equivalent or tonne of coal equivalent (TCE), a conventional value of 7 Gcal (IT) = 29.3076 GJ.

ton of oil equivalent

- A ton of oil equivalent or tonne of oil equivalent (TOE), a conventional value of 10 Gcal (IT) = 41.868 GJ ≈ 10.0067 ton of TNT. See also GTOE.

Unit of power

Miscellaneous tons

External links

Long ton

A long ton (sometimes known as a gross ton or weight ton) is the name used in the US for the unit called the "ton" in the avoirdupois or Imperial system of measurements, as used (alongside the metric system) in the United Kingdom and several other Commonwealth countries. It is equal to 2240 pounds (exactly 1016.0469088 kilograms). It has some limited use in the US, most commonly in measuring the displacement of ships. The standard ton in the US measurement system is the "short ton", equal to 2000 pounds (exactly 907.18474 kg). Both long and short tons are defined as 20 hundredweights, but a hundredweight is 112 pounds (which is equal to 8 stone) in the Imperial system (long or gross hundredweight) and 100 pounds in the US system (short or net hundredweight). The spelling "tonne" denotes the metric tonne of 1000 kilograms (approximately 2204.623 pounds). See also:
- short ton
- tonne Category:Units of mass Ton, long Ton, long

Tonnage

Tonnage is a measure of the size or cargo capacity of a ship. Tonnage varies in meaning depending on the vessel. It can refer to the weight of a loaded or empty vessel, or to its volume or its cargo volume. Measurement of tonnage can be less than straightforward, not least because it is used to assess fees on commercial shipping. Port authorities, naval architects, and owners may have different approaches to calculating tonnage. Gross Tonnage or Gross Register Tonnage is the internal volume of a vessel plus the space on exposed cargo decks (with some exemptions, depending on the assessing body). It (or Net Tonnage, below) is used for calculating canal transit or harbor fees, and is often expressed in gross tons, measurement tons, or cubic meters. Net Tonnage or Net Register Tonnage is Gross Tonnage less the volume of spaces that will not hold cargo (e.g. engine compartment, helm station, crew spaces, etc., again with differences depending on which port or country is doing the calculations). It represents the volume of the ship available for transporting freight or passengers. Register Tonnage calculations are complex. A hold can, for instance, be assessed for grain (accounting for all the air space in the hold) or for bales (exempting the spaces between structural frames). Net Tonnage is often expressed in gross tons, measurement tons, or cubic meters. Displacement Tonnage is the actual weight of the vessel and its contents. It is often used to rate naval vessels, since their weight is fairly constant and they are not subject to the kinds of port fees that are calculated on Register Tonnage. It is often expressed in long tons or in metric tons. Deadweight Tonnage is the maximum weight that a ship can safely carry when fully loaded. It includes the crew, passengers, cargo, fuel, water, and stores. Like Displacement Tonnage, it is often expressed in long tons or in metric tons.
- A measurement ton measures space. Its value is 100 cubic feet (2.832 cubic meters).
- A freight ton also measures space. Its value is 40 cubic feet (1.133 cubic meter).
- A long ton measures weight. Its value is 2,240 pounds (1,016.05 kg). (The common ton in use in the Imperial and U.S. systems of measurements is the short ton of 2,000 pounds (907.18 kg).)
- A metric ton (commonly written tonne and abbreviated t) equals 1,000 kilograms. It is not difficult to estimate a ship's actual weight (displacement tonnage). Estimate how many cubic feet of water it is displacing (the volume of the hull lying below the water). Multiply by 64 (the weight of one cubic foot of seawater) to get the weight of the ship in pounds. Or divide the cubic feet by 35 to go directly to the weight in long tons. ---- Historically, Tonnage and Poundage was the tax on tuns (casks) of wine shipped to England, mostly from Spain and Portugal, under a subsidy granted to the English crown by Parliament starting in the 14th century.

Conversion of units

This article lists conversion factors between a number of units of measurement.

Conversion techniques

The simplest way to convert from one unit to another is to carry through the units themselves in the mathematical operation. To illustrate this process, consider the following examples. You would like to convert 6 feet into metres. Consulting the table below and finding that one foot is exactly 0.3048 metre, you can now perform the mathematical conversion: 6 ft × 0.3048 m/ft = 1.8288 m Notice that the "foot" units canceled out, leaving only metres, the desired result. (Since 0.3048 metre per foot have infinite precision, the precision of the answer is determined by the precision of the 6 ft figure; if, for example, you are defining the fathom, expressing it with 5 significant figures is correct. But if the 6 ft figure is a measurement, the result needs to be rounded appropriately.) Say your height is 183 centimetres, and you wish to convert this into inches: 183 cm / (2.54 cm/in) = 72.0 in To check our answer, we convert this result back into feet: 72 in / (12 in/ft) = 6.0 feet which confirms the earlier result. Multiple units can be manipulated in the same fashion: 7 mi/s × 1.609344 km/mi × 3600 s/h = 40,000 km/h Thus, Earth escape velocity is about 7 miles per second, or 40,000 kilometres per hour. Notice that since the calculation started with one significant figure (the 7), the answer also has one significant figure (the 4 in 40,000). Deciding whether to multiply or divide is determined by looking at the units and deciding which ones you want to "get rid" of. In the conversion just above, if we had divided by 3600 s/h instead of multiplying, the result would have come out in kilometre-hours per square second, clearly an incorrect and meaningless result.

Rounding of results

An important thing to remember is that the process of making a conversion cannot give you any more precise results than what you started with. While many of the conversion factors given in the tables below are exact, and others while not exact contain many significant digits, all the numbers you get after performing calculations on a calculator or with pencil and paper are not meaningful. After using these conversion factors, be sure to round off the results appropriately.

Tables of conversion factors

Key:
≡ — definition
= — exactly equal to
≈ — approximately equal to
(digits) — indicates the digits repeat infinitely

Length

Area

Volume

Angle

Mass

| | ≡ 60 kg | = 60 kg |----- | quintal (metric) || q | | ≡ 100 kg |----- | wey || | ≡ 252 lb = 18 st | = 114.305 277 24 kg (variants exist) |----- | long quarter|| | ≡ ¼ long tn | = 254.011 727 2 kg |----- | kip || kip | ≡ 1000 lb av | = 453.592 37 kg |----- | short ton || sh tn | ≡ 2000 lb | = 907.184 74 kg |----- | tonne (mts unit) || t | | ≡ 1000 kg |----- | long ton|| long tn or ton | ≡ 2240 lb | = 1016.046 908 8 kg |----- | barge || | ≡ 22 ½ sh tn | = 20,411.656 65 kg |{| class="wikitable" |+ Time, t !Name of unit !Symbol !Definition !Relation to SI units |----- | second || s | | (SI base unit) |----- | Planck time || | ≡ √(G ℏ/c⁵) | ≈ 1.351 211 818×10^-43 s |----- | atomic unit of time || au | ≡ a₀/(α·c) | ≈ 2.418 884 254×10^-17 s |----- | svedberg || S | ≡ 10^-13 s | = 100 fs |----- | shake || | ≡ 10^-8 s | = 10 ns |----- | sigma || | ≡ 10^-6 s | = 1 μs |----- | jiffy || | ≡ 1/60 s | ≈ 16.666 667 ms |----- | jiffy (alternate) || | ≡ 1/100 s | ≈ 10 ms |----- | helek || | ≡ 1/1080 h | ≈ 3.333333 s |----- | minute || min | | ≡ 60 s |----- | hour || h | ≡ 60 min | = 3600 s |----- | day || d | ≡ 24 h | = 86 400 s |----- | week || wk | ≡ 7 d | = 604 800 s |----- | fortnight || | ≡ 2 wk | = 1 209 600 s |----- | month (hollow) || mo | ≡ 29 d | = 2 505 600 s |----- | month (full) || mo | ≡ 30 d | = 2 592 000 s |----- | year (Calendar) || a or y | ≡ 365 d | = 31 536 000 s |----- | year (Gregorian) || a or y | ≡ 365.2425 d | = 31 556 952 s |----- | year (Julian) || a or y | ≡ 365.25 d | = 31 557 600 s |----- | sidereal year || a or y | ≡ 365.256363 d | = 31 558 149.76 s |----- | lustre; lustrum || | ≡ 5 a of 365 d | = 1.5768×10⁸ s |----- | octaeteris || | ≡ 8 a of 365 d | = 2.522 88×10⁸ s |----- | decade || | ≡ 10 a of 365 d | = 3.1536×10⁸ s |----- | enneadecaeteris; Metonic cycle || | ≡ 110 mo (hollow) + 125 mo (full) = 19 a of 365 d | = 5.996 16×10⁸ s |----- | Callippic cycle || | ≡ 441 mo (hollow) + 499 mo (full) = 76 a of 365.25 d | = 2.398 377 6×10⁹ s |----- | century (Calendar) || | ≡ 100 a of 365 d | = 3.1536×10⁹ s |----- | century (Julian) || | ≡ 100 a of 365.25 d | = 3.155 76×10⁹ s |----- | Hipparchic cycle || | ≡ 4 Callippic cycles - 1 d | = 9.593 424×10⁹ s |----- | millennium (Calendar) || | ≡ 1000 a of 365 d | = 3.1536×10¹⁰ s |----- | millennium (Gregorian) || | ≡ 1000 a of 365.2425 d | = 3.155 695 2×10¹⁰ s |----- | millennium (Julian) || | ≡ 1000 a of 365.25 d | = 3.155 76×10¹⁰ s |----- | Sothic cycle || | ≡ 1461 a of 365 d | = 4.607 409 6×10¹⁰ s |{| class="wikitable" |+ Speed, v !Name of unit !Symbol !Definition !Relation to SI units |----- | metre per second (SI unit)|| m/s | | ≡ 1 m/s |----- | foot per hour || fph | ≡ 1 ft/h | ≈ 8.466 667×10^-5 m/s |----- | furlong per fortnight || | ≡ ½ fur/wk | ≈ 1.663 095×10^-4 m/s |----- | inch per minute || ipm | ≡ 1 in/min | ≈ 4.23 333×10^-4 m/s |----- | foot per minute || fpm | ≡ 1 ft/min | = 5.08×10^-3 m/s |----- | inch per second || ips | ≡ 1 in/s | = 2.54×10^-2 m/s |----- | kilometre per hour || km/h | ≡ 1 km/h | ≈ 2.777 778×10^-1 m/s |----- | foot per second || fps | ≡ 1 ft/s | = 3.048×10^-1 m/s |----- | mile per hour || mph | ≡ 1 mi/h | = 0.447 04 m/s |----- | knot || kn | ≡ 1 NM/h = 1.852 km/h | ≈ 0.514 444 m/s |----- | knot (Admiralty) || kn | ≡ 1 NM (Adm)/h = 1.853 184 km/h | ≈ 0.514 773 m/s |----- | mile per minute || mpm | ≡ 1 mi/min | = 26.8224 m/s |----- | mile per second || mps | ≡ 1 mi/s | = 1.609 344 km/s |----- | speed of light in vacuum || c | | ≡ 2.997 924 58×10⁸ m/s |{| class="wikitable" |+ Acceleration, a !Name of unit !Symbol !Definition !Relation to SI units |----- | metre per second squared (SI unit)|| m/s² | | ≡ 1 m/s² |----- | foot per hour per second || fph/s | ≡ 1 ft/h·s | ≈ 8.466 667×10^-5 m/s² |----- | inch per minute per second || ipm/s | ≡ 1 in/min·s | ≈ 4.233 333×10^-4 m/s² |----- | foot per minute per second || fpm/s | ≡ 1 ft/min·s | = 5.08×10^-3 m/s² |----- | galileo || Gal | ≡ 1 cm/s² | = 10^-2 m/s² |----- | inch per second squared || ips² | ≡ 1 in/s² | = 2.54×10^-2 m/s² |----- | foot per second squared || fps² | ≡ 1 ft/s² | = 3.048×10^-1 m/s² |----- | mile per hour per second || mph/s | ≡ 1 mi/h·s | = 4.4704×10^-1 m/s² |----- | knot per second || kn/s | ≡ 1 kn/s | ≈ 5.144 444×10^-1 m/s² |----- | standard gravity || g | | ≡ 9.806 65 m/s² |----- | mile per minute per second || mpm/s | ≡ 1 mi/min·s | = 26.8224 m/s² |----- | mile per second squared || mps² | ≡ 1 mi/s² | = 1.609 344×10³ m/s² |{| class="wikitable" |+ Force, F !Name of unit !Symbol !Definition !Relation to SI units |----- | newton (SI unit) || N | ≡ kg·m/s² | |----- | atomic unit of force || au | ≡ m_e·α²·c²/a₀ | ≈ 8.238 722 241×10^-8 N |----- | dyne (cgs unit) || dyn | ≡ g·cm/s² | = 10^-5 N |----- | gravet || | ≡ g × 1 g | = 9.806 65 mN |----- | poundal || pdl | ≡ 1 lb·ft/s² | = 0.138 254 954 376 N |----- | ounce-force || ozf | ≡ g × 1 oz | = 0.278 013 850 953 781 2 N |----- | pound-force || lbf | ≡ g × 1 lb | = 4.448 221 615 260 5 N |----- | kilogram-force; kilopond; grave || kgf; kp | ≡ g × 1 kg | = 9.806 65 N |----- | sthene (mts unit) || sn | ≡ 1 t·m/s² | = 1 kN |----- | kip; kip-force || kip; kipf; klbf | ≡ g × 1000 lb | = 4.448 221 615 260 5 kN |----- | ton-force || tnf | ≡ g × 1 sh tn | = 8.896 443 230 521 kN