The ton is a unit of measure. It has a long history and has acquired a number of meanings and uses over the years. It is used principally as a unit of weight, and as a unit of volume. It can also be used as a measure of energy, for truck classification, or as a colloquial term.

It is derived from the tun, the term applied to a barrel of the largest size. This could contain a volume between 210 and 256 gallons (800 to 1000 L), which could weigh around 2,000 pounds (900 kg) and occupy some 60 cubic feet (1700 L) of space.[1]

In the United Kingdom, the ton is a unit of measure which, when it ceased to be legal for trade in 1985, was defined in British legislation as being a weight or mass equal to 2,240 pounds (1,016 kg) (avoirdupois pounds).[2] In the United States and Canada,[3] however, a ton is defined to be 2,000 pounds (907 kg). To avoid confusion, the former is more specifically referred to as a "long ton" and the latter, a "short ton"; neither should be confused with the metric ton (tonne), which is 1,000 kilograms (2,205 lb). While they do vary, a ton is generally one of the heaviest units of weight or mass referred to in colloquial speech.

The term "ton" is also used to refer to a number of units of volume, ranging from 35 to 100 cu ft (around 1000 to 2800 L) in capacity.

It can also be used as a unit of energy, expressed as an equivalent of coal burnt, TNT detonated, or in refrigeration, ice melted.


Units of mass/weight

There are several similar units of mass or volume called the ton:

Full name(s) Common name Quantity Notes
long ton,[4] weight ton, gross ton "ton" (UK) 2,240 lb (1,016.047 kg) Used in countries such as the United Kingdom that formerly used the Imperial system
short ton,[5] net ton "ton" (US) 2,000 lb (907.1847 kg) Used in North America
tonne[6] "metric ton"

(mainly US)

1,000 kg (2,204.623 lb) Defined in the International System of Units. In the UK, Canada, Australia, and other areas that had used the Imperial system, the tonne is the form of ton legal in trade. Less than 2% different from the long ton.
ton shortweightnote 1 2240 lb Used in the iron industry in the 17th and 18th centuries.
ton longweightnote 1 2400 lbnote 2 Used in the iron industry in the 17th and 18th centuries.
Note 1: The longweight and shortweight tons were used as a means of making an allowance for wastage in an industrial process. The workman is provided with a longweight ton and is expected to return a shortweight ton of processed product. These measures were particulary used in the operation of hammering iron blooms into shape.[7]
Note 2: In other industries, a different longweight ton might be used. Coal miners delivered coal to the surface in longweight tons but were paid only for a shortweight ton. This was supposedly to allow for "dirt" (non-coal rocks) in the output. Mine owners, however, were free to set the value of the longweight ton at a value of their own choosing, and in at least some cases, it was set to 25 cwt (2800 lb) compared to the 20 cwt shortweight ton. This was a source of discontent amongst the miners who saw the practice as unfairly in favour of the mine owners.[8]
  • The long ton is used for petroleum products such as aviation fuel.
  • Deadweight ton (abbreviation 'DWT' or 'dwt') is a measure of a ship's carrying capacity, including bunker oil, fresh water, ballast water, crew and provisions. It is expressed in tonnes (1000 kg) or long tons (2240 pounds, about 1016 kg). This measurement is also used in the U.S. tonnage of naval ships.
  • Increasingly, tonnes are being used rather than long tons in measuring the displacement of ships. See tonnage.
  • Harbour ton used in South Africa in the 20th century, 2000 pounds or one short ton.

Both the long ton and the short ton are composed of 20 hundredweight, being 112 and 100 pounds respectively. Prior to the 15th century in England, the ton was composed of 20 hundredweight, each of 108 lb, giving a ton of 2,160 pounds (980 kg).[citation needed]

Assay ton (abbreviation 'AT') is not a unit of measurement, but a standard quantity used in assaying ores of precious metals; it is 29 16 grams (short assay ton) or 32 23 grams (long assay ton), the amount which bears the same ratio to a milligram as a short or 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 or long ton of ore.

In documents that predate 1960 the word ton is sometimes spelled tonne, but in more recent documents tonne refers exclusively to the metric ton.

In nuclear power plants tHM and MTHM mean tonnes of heavy metals, and MTU means tonnes of uranium. In the steel industry, the abbreviation THM means 'tons/tonnes hot metal', which refers to the amount of liquid iron or steel that is produced, particularly in the context of blast furnace production or specific consumption.

A dry ton or dry tonne has the same mass value, but the material (sludge, slurries, compost, and similar mixtures in which solid material is soaked with or suspended in water) has been dried to a relatively low, consistent moisture level (dry weight). If the material is in its natural, wet state, it is called a wet ton or wet tonne.

Units of volume

The displacement ton is a unit of volume used for calculating the displacement of a ship.[9] While displacement is a measure of a ships weight, being the volume of water displaced multiplied by its density and measured in long tons (tons displacement), the displacement ton is the standard volume of water representing one ton displacement.[10] It equates to 35 cubic feet (0.9911 m3) of sea water at average density, being slightly less than the 224 imperial gallons, of the water ton (qv).[citation needed] It is usually abbreviated as DT.

One measurement ton or freight ton is equal to 40 cubic feet (1.133 m3), but historically it has had several informal definitions. It is sometimes abbreviated as "MTON".[11][12][13][14] The freight ton represents the volume of a truck, train or other freight carrier. In the past it has been used for a cargo ship but the register ton is now preferred. It is correctly abbreviated as "FT"[citation needed] but some users are now using freight ton to represent a weight of 1 tonne (1,000 kg; 2,205 lb), thus the more common abbreviations are now M/T, MT, or MTON (for measurement ton), which still cause it to be confused with the tonne, or even the megatonne.

The register ton is a unit of volume used for the cargo capacity of a ship, defined as 100 cubic feet (2.832 m3). It is often abbreviated RT or GRT for gross registered ton (The former providing confusion with the refrigeration ton). It is known as a tonneau de mer in Belgium, but, in France, a tonneau de mer is 1.44 cubic metres (50.85 cu ft).

The Panama Canal/Universal Measurement System (PC/UMS) is based on net tonnage, modified for Panama Canal billing purposes. PC/UMS is based on a mathematical formula to calculate a vessel's total volume; a PC/UMS net ton is equivalent to 100 cubic feet of capacity.[15]

The water ton was formerly used in Great Britain and is equal to 224 imperial gallons (35.96 cu ft; 1.018 m3), the volume occupied by a mass of 1 long ton (2,240 lb; 1,016 kg) under the conditions that define 1 imperial gallon (1.201 US gal; 4.546 L).[citation needed]

Units of energy and power

Ton of TNT

  • A ton of TNT or tonne of TNT is a unit of energy equal to 109 (thermochemical) calories, also known as a gigacalorie (Gcal), equal to 4.184 gigajoules (GJ).
  • A kiloton of TNT or kilotonne of TNT is a unit of energy equal to 1012 calories, also known as a teracalorie (Tcal), equal to 4.184 terajoules (TJ).
  • A megaton of TNT (1,000,000 metric tonnes) or megatonne of TNT is a unit of energy equal to 1015 calories, also known (infrequently) as a petacalorie (Pcal), equal to 4.184 petajoules (PJ).

Note that these are small calories (cal). The dietary calorie (Cal) is distinct and equal to one kilocalorie (Kcal), and is gradually being replaced by the latter correct term.

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 (1 kcal or 4.184 kJ) 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).[16][17] 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.

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.


The unit ton is used in refrigeration and air conditioning to measure heat absorption. Prior to the introduction of mechanical refrigeration, cooling was accomplished by delivering ice. Installing one ton of refrigeration replaced the daily delivery of one ton of ice.

  • In North America, a standard ton of refrigeration is 12,000 BTU/h (3,517 W). "The heat absorption per day is approximately the heat of fusion of 1 ton of ice at 32 °F (0 °C)."[18] This is approximately the power required to melt one short ton (2,000 lb or 907 kg) of ice at 0 °C (32 °F) in 24 hours, thus representing the delivery of 1 ton of ice per day.
  • A less common usage is the power required to cool 1 long ton (2,240 lb or 1,016 kg) of water by 1 °F (0.556 °C) every 10 minutes = 13,440 BTU/h ≈ 3939 W.[19][20]

A refrigeration ton should be regarded as power produced by a chiller when operating in standard ARI conditions, which are typically 44 °F (7 °C) for chilled water unit, and 95 °F (35 °C) air entering the condenser. This is commonly referred to as "true ton". Manufacturers can also provide tables for chillers operating at other chilled water temperature conditions (as 65 °F or 18 °C) which can show more favorable data, which are not valid when making performance comparisons among units unless conversion rates are applied.[citation needed]

The refrigeration ton is commonly abbreviated as RT.

Informal tons

  • Ton is also used informally, often as slang, to mean a large amount of something (material or not), for example, "Man, I just ate a ton of french fries back there".
  • In Britain, a ton is colloquially used to refer to 100 of a given unit. Ton can thus refer to a speed of 100 miles per hour, and is prefixed by an indefinite article, e.g. "Lee was doing a ton down the motorway"; to money e.g. "How much did you pay for that?" "A ton" (£100); to 100 points in a game e.g. "Eric just threw a ton in our darts game" (in some games, e.g. cricket, more commonly called a century); or to a hundred of pretty much anything else.

See also


  1. ^ "Naval Architecture for All". United States Bureau of Transportation Statistics. Retrieved October 13, 2008. . "Historically, a very important and standard cargo for European sailing vessels was wine, stored and shipped in casks called tuns. These tuns of wine, because of their uniform size and their universal demand, became a standard by which a ship's capacity could be measured. A tun of wine weighed approximately 2,240 pounds, and occupied nearly 60 cubic feet." (Gillmer, Thomas (1975). Modern Ship Design. United States Naval Institute.) "Today the ship designers standard of weight is the long ton which is equal to 2,240 pounds."
  2. ^ "Weights and Measures Act 1985". Her Majesty's Stationery Office. 1985-10-30. Retrieved 2010-02-03. 
  3. ^ "Weights and Measures Act: Canadian units of measure". Department of Justice. Retrieved 2011-07-06. 
  4. ^
  5. ^
  6. ^
  7. ^ Chris Evans, Göran Rydén, Baltic iron in the Atlantic world in the eighteenth century, p.257, Brill 2007 ISBN 9004161538
  8. ^ "Report of the select committee on mines", Reports from Committees 1866, vol.9, pp.134-136, London: House of Commons, 23 July 1866
  9. ^ Displacement ton Dictionary of international trade retrieved 22July2010
  10. ^ ton, displacement Dictionary of international trade retrieved 22July2010
  11. ^ "MSC 2003 in Review - Financial and Statistical Review". 2003-09-30. Retrieved 2010-07-31. 
  12. ^ Military Surface Deployment and Distribution Command, 2009
  13. ^ "182 F.2d 916". Retrieved 2010-07-31. 
  14. ^ "Pos Ttariff General Definitions". Retrieved 2010-07-31. 
  15. ^ Panama Canal Tolls, Panama Canal Authority. Retrieved 10 May 2006.
  16. ^ GC(42)/INF/3 - Measures to Strengthen Co-operation in Nuclear, Radiation and Waste Safety
  17. ^ Radioactive residues of the Cold War period
  18. ^ Marks' Standard handbook for Mechanical Engineers, 8th Ed., McGraw Hill, p. 19–3
  19. ^ "ton (of refrigeration)". Retrieved 2006-09-01. 
  20. ^ Gérard P. Michon. "Measurements and Units". Retrieved 2006-09-01. 

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