Ton

Categories: Units of mass | Units of volume | Customary units in the United States | Imperial units

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 many meanings of ton:

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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.

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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
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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: 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.

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Unit of energy

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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, with a lowercase initial letter. The dietary Calorie, with an uppercase initial letter, is equal to one thousand thermal calories. (It is the lowercase thermal calorie which by definition heats a gram of water by one Celsius degree.)


Early values for the explosive energy released by 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: [1], [2]). The definition applies for both spellings: ton of TNT and tonne of TNT.


Sample terms:

'grams TNT' Symbol 'tons TNT' Symbol Energy
gram of TNT g 4.184 × 103 J
kilogram of TNT kg 4.184 × 106 J
megagram of TNT Mg ton of TNT t 4.184 × 109 J
gigagram of TNT Gg kiloton of TNT kt 4.184 × 1012 J
teragram of TNT Tg megaton of TNT Mt 4.184 × 1015 J
petagram of TNT Pg gigaton of TNT Gt 4.184 × 1018 J
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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.
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ton of oil equivalent

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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
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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
  • 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.
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See also

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External links

de:Tonne eo:tuno es:tonelada et:Tonn fr:Tonne ko:톤 nl:Ton ja:トン pl:tona simple:ton sl:tona zh:吨