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 tonne of 1000 kilograms (or the associated obsolete force unit) when used in non-American English, is a direct borrowing from the French language.

Units of mass

There are two similar units of mass called the ton:

1. long ton (simply ton in countries such as the United Kingdom which formerly used the Imperial system of weights and measures) is a weight ton or gross ton, and is 2,240 lb (exactly 1,016.0469088 kg). In the UK and most of the areas which used the Imperial system, the metric tonne (1000 kg), which it is conveniently very similar to—less than 2% difference, is the only form of ton legal for trade.
   • As a displacement ton the long ton is normally measured as the mass of 35 cubic feet of sea water. Increasingly, metric tonnes are being used rather than long tons in measuring the displacement of ships. See tonnage.
   • The long ton is used for petroleum products such as aviation fuel.
   • Deadweight ton (abbreviation 'dwt') for the capacity of a ship in the number of long tons (2,240 pounds). This measurement is also used in the U.S. tonnage of naval ships.
2. short ton (usually called simply ton in the USA or sometimes called a net ton) = 2000 lb (exactly 907.18474 kg).
   • Harbour ton used in South Africa in the 20th century, equal to 2000 pounds or one short ton.

Both the long ton and the short ton are composed of twenty hundredweights, each having different values for the hundredweight (112 and 100 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.

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.

In documents which predate 1960 the word ton may be spelt tonne however in more recent documents the spelling tonne refers exclusively to the metric tonne.

In the context of nuclear power plants, tHM and MTHM mean (metric) tonnes of heavy metal, and MTU means metric tonnes of uranium.

A dry ton or dry tonne has the same mass value, but the material has been dried to a relatively low, consistent moisture level.

Units of force

There are also the units of force based on each of these three mass units, but none are acceptable for use with SI. The metric tonne force (tonne force), like the kilogram force, is no exception. Only the metric ton or tonne as a unit of mass is 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

Also see 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 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, is 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.

(Note that volume tons are units of convenience used in shipping and are not useful in science except that they are exactly defined.)

Units 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 (not capitalized). The dietary Calorie (capitalized) 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/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 they 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 W
  • The power required to cool 1 long ton of water by 1 °F every 10 minutes = 13,440 BTU/h ≈ 3,938.87518 W
  • A corresponding unit of energy equal to that power for a period of a day, or 24h × 12,000 BTU/h = 288,000 BTU ≈ 303,856,086 J

Miscellaneous tons

• Ton is also used informally to mean a large amount of something (material or not).

• 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.

See also

• Conversion of units
• Medieval weights and measures
• Ancient weights and measures
• English unit
• Imperial unit
• U.S. customary unit

The ton also refers to a group of people, the English aristocracy, during the Georgian period, who referred to themselves as the ton, presumably to imply they had a lot of weight.

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

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