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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 a ton of tons:


Units of mass

There are three similar units of mass called the ton or tonne:

  • tonne or metric ton = 1000 kg (2204.6 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) = 907.185 kg (2000 lb).
  • long ton (or weight ton) in common use just ton = 1016.047 kg (2240 lb), is an avoirdupois unit commonly used in the UK and British areas of influence. The UK has now adopted 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 (abrv. '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 still composed of twenty hundredweights, but each was 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 uranium.

Assay ton (abrv. '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 = 8.89644 kilonewtons (kN)
  • 1 long ton force = 2240 lbf = 9.96402 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:

The amount of fresh water at 4 C displaced by one measurement ton has a mass similar to the ton masses listed above: 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 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 m and orders of magnitude (volume) for a comparison with other volumes.

Units of energy and 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 = 3.516853 kW (kilowatts)
  • 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 MJ (megajoules)
  • A ton of TNT or tonne of TNT is equal to 1,000,000 grams (1 metric tonne) at a conventional energy value of 1000 small (thermochemical) calories per gram, thus 1 gigacalorie, or 4.184 gigajoules. See also megaton.
  • A ton of coal equivalent or tonne of coal equivalent (TCE), a conventional value of 7 Gcal (IT) = 29.3076 GJ.

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 mi/h
    • 100 km/h
  • In money, a ton is slang for 100 GBP (pounds sterling) - this is primarily used in London, England.
  • In darts, a ton is a score of 100 or more points with three darts.
  • In motor vehicles, many trucks are classified into groups loosely related to their carrying capacity as 1/2 ton, 3/4 ton, 2 1/2 ton (deuce-and-a-half in U.S. military slang), 5 ton, etc.

See also

External links

Last updated: 10-20-2005 02:13:31
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