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One-ton weight.svg
General information
Unit system
Unit of Mass
1 in ...... is equal to ...
   SI derived unit   1,016.0469 kg (long ton)
   SI derived unit   907.1847 kg (short ton)

Ton is any of several units of measure of mass, volume or force. It has a long history and has acquired several meanings and uses.


As a unit of mass, ton can mean:

Its original use as a unit of volume has continued in the capacity of cargo ships and in units such as the freight ton and a number of other units, ranging from 35 to 100 cubic feet (0.99 to 2.83  m3 ) in size. Recent specialized uses include the ton as a means of truck classification. It can also be used as a unit of energy, or in refrigeration as a unit of power, sometimes called a ton of refrigeration .

Because the ton (of any system of measuring weight) is usually the heaviest unit named in colloquial speech, its name also has figurative uses, singular and plural, informally meaning a large amount or quantity, or to a great degree, as in "There's a ton of bees in this hive," "We have tons of homework," and "I love you a ton."


The ton is derived from the tun , the term applied to a cask of the largest capacity. This could contain a volume between 175 and 213 imperial gallons (210 and 256  US gal ; 800 and 970  L ), which could weigh around 2,000 pounds (910  kg ) and occupy some 60 cubic feet (1.7  m3 ) of space. [1]

Units of mass/weight

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

Full name(s)Common nameQuantity [lower-alpha 1] SymbolNotes
long ton [2] "ton" (United Kingdom)2,240  lb (1,016.0469088  kg )LTUsed in Ireland and Commonwealth countries that formerly used, or still use the Imperial system
short ton [3] "ton" (United States)2,000 lb (907.18474 kg)tn [4] or st [5] Used in the United States and in some industries in Canada
tonne [6]
(equivalent to one megagram)
"metric ton"
1,000 kg (about 2,204.6226 lb)t [6] Defined in the International System of Units. Used worldwide.
shortweight ton [lower-alpha 2] 2,240 lbUsed in the iron industry in the 17th and 18th centuries.
longweight ton [lower-alpha 2] 2,400 lb [lower-alpha 3]
  1. Conversions are exact unless otherwise stated.
  2. 1 2 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 particularly used in the operation of hammering iron blooms into shape. [7]
  3. 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 (2,800 lb) compared to the 20 cwt shortweight ton. This was a source of discontent amongst the miners who saw the practice as unfair in favour of the mine owners. [8]

The difference between the short ton and the other common forms ("long" and "metric") is about 10%, while the metric and long tons differ by less than 2%.

The metric tonne is usually distinguished by its spelling when written, but in the United States and United Kingdom, it is pronounced the same as ton, hence is often spoken as "metric ton" when it is necessary to make the distinction. In the United Kingdom the final "e" of "tonne" can also be pronounced ( /ˈtʌni/ ), [9] . In Australia, it is pronounced /tɒn/ .

In Ireland and most members of the Commonwealth of Nations, a ton is defined as 2,240 pounds (1,016.04691 kg). [lower-alpha 1] [10]

In the United States and Canada, [11] a ton is defined as 2,000 pounds (907.18474 kg).

Other units of mass/weight

Assay ton (abbreviation 'AT') is not a unit of measurement but a standard quantity used in assaying ores of precious metals. A short assay ton is approximately 29.17 g (1.029 oz) and a long assay ton is approximately 32.67 g (1.152 oz). [12] [ citation needed ] These amounts bear the same ratio to a milligram as a short or long ton bears to a troy ounce. Therefore, the number of milligrams of a particular metal found in a sample weighing one assay ton gives the number of troy ounces of metal contained in a ton of ore.

In documents that predate 1960 the word ton is sometimes spelled tonne,[ citation needed ] 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.


Both the UK definition of long ton and US definition of short ton have similar underlying bases. Each is equivalent to 20 hundredweight; however, they are long 51 kilograms (112 lb) or short hundredweight 45 kilograms (100 lb), respectively.

Before the 20th century there were several definitions. Prior to the 15th century in England, the ton was 20 hundredweight, each of 108 lb, giving a ton of 2,160 pounds (980 kg).[ citation needed ] In the 19th century in different parts of Britain, definitions of 2,240, or 2,352, or 2,400 lb were used, with 2,000 lb for explosives; the legal ton was usually 2,240 lb. [13]

In the United Kingdom, Canada, Australia, and other areas that had used the imperial system, the tonne is the form of ton legal in trade.

Units of volume

The displacement, essentially the weight, of a ship is traditionally expressed in long tons. [14] To simplify measurement it is determined by measuring the volume, rather than weight, of water displaced, and calculating the weight from the volume and density. [15] For practical purposes the displacement ton (DT) is a unit of volume, 35 cubic feet (0.9911 m3), the approximate volume occupied by one ton of seawater (the actual volume varies with salinity and temperature). [16] It is slightly less than the 224 imperial gallons (1.018 m3) of the water ton (based on distilled water).

One measurement ton or freight ton is equal to 40 cubic feet (1.133 m3), but historically it has had several different definitions. It is used to determine the amount of money to be charged in loading, unloading, or carrying different sorts of cargo. In general if a cargo is heavier than salt water, the actual tonnage is used. If it is lighter than salt water, e.g. feathers, freight is calculated using Measurement Tons of 40 cubic feet. [17] [18] [19] [20]

Gross tonnage and net tonnage are volumetric measures of the cargo-carrying capacity of a ship.

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. [21]

The water ton is used chiefly in Great Britain, in statistics dealing with petroleum products, and is defined as 224 imperial gallons (35.96 cu ft; 1.018 m3), [22] the volume occupied by 1 long ton (2,240 lb; 1,016 kg) of water under the conditions that define the imperial gallon.

Units of energy and power

Ton of TNT

These are small calories (cal). The large or dietary calorie (Cal) is 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 1,000 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). [23] [24] 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.

Tonne of oil equivalent

A tonne of oil equivalent (toe), sometimes ton of oil equivalent, is a conventional value, based on the amount of energy released by burning one tonne of crude oil. The unit is used, for example, by the International Energy Agency (IEA), for the reported world energy consumption as TPES in millions of toe (Mtoe). [25]

Unit conversion factors for toe
toe MWh GJ Gcal million Btu tce
Source: conversion factors as used by the IEA [26]

Other sources convert 1 toe into 1.28 tonne of coal equivalent (tce). [27] 1 toe is also standardized as 7.33 barrel of oil equivalent (boe). [28]

Tonne of coal equivalent

A tonne of coal equivalent (tce), sometimes ton of coal equivalent, is a conventional value, based on the amount of energy released by burning one tonne of coal. Plural name is tonnes of coal equivalent.

Unit conversion factors for tce
tce MWh GJ Gcal million Btu toe
Source: conversion factors as used by the IEA [26]


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

The refrigeration ton is commonly abbreviated as RT.

Informal tons

See also

Related Research Articles

The joule is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of one newton displaces a mass through a distance of one metre in the direction of that force. It is also the energy dissipated as heat when an electric current of one ampere passes through a resistance of one ohm for one second. It is named after the English physicist James Prescott Joule (1818–1889).

<span class="mw-page-title-main">Tonne</span> Metric unit of mass equivalent to 1,000 kilograms or 1 megagram

The tonne is a unit of mass equal to 1,000 kilograms. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton in the United States to distinguish it from the non-metric units of the short ton and the long ton. It is equivalent to approximately 2,204.6 pounds, 1.102 short tons, and 0.984 long tons. The official SI unit is the megagram (Mg), a less common way to express the same amount.

<span class="mw-page-title-main">United States customary units</span> System of units of measurement commonly used in the United States

United States customary units form a system of measurement units commonly used in the United States and most U.S. territories, since being standardized and adopted in 1832. The United States customary system developed from English units that were in use in the British Empire before the U.S. became an independent country. The United Kingdom's system of measures was overhauled in 1824 to create the imperial system, which was officially adopted in 1826, changing the definitions of some of its units. Consequently, while many U.S. units are essentially similar to their imperial counterparts, there are noticeable differences between the systems.

The long ton, also known as the imperial ton or displacement ton, is a measurement unit equal to 2,240 pounds (1,016.047 kg). It is the name for the unit called the "ton" in the avoirdupois system of weights or Imperial system of measurements. It was standardised in the 13th century. It is used in the United Kingdom and several other Commonwealth of Nations countries alongside the mass-based tonne defined in 1799, as well as in the United States for bulk commodities.

<span class="mw-page-title-main">Twenty-foot equivalent unit</span> Unit of cargo capacity

The twenty-foot equivalent unit is a general unit of cargo capacity, often used for container ships and container ports. It is based on the volume of a 20-foot-long (6.1 m) intermodal container, a standard-sized metal box which can be easily transferred between different modes of transportation, such as ships, trains, and trucks.

<span class="mw-page-title-main">Bushel</span> Unit of volume with numerous different definitions

A bushel is an imperial and US customary unit of volume based upon an earlier measure of dry capacity. The old bushel is equal to 2 kennings (obsolete), 4 pecks, or 8 dry gallons, and was used mostly for agricultural products, such as wheat. In modern usage, the volume is nominal, with bushels denoting a mass defined differently for each commodity.

<span class="mw-page-title-main">Hundredweight</span> Unit of weight or mass, with differing values

The hundredweight, formerly also known as the centum weight or quintal, is a British imperial and United States customary unit of weight or mass. Its value differs between the United States customary and British imperial systems. The two values are distinguished in American English as the short and long hundredweight and in British English as the cental and imperial hundredweight.

The short ton is a measurement unit equal to 2,000 pounds (907.18 kg). It is commonly used in the United States, where it is known simply as a ton; however, the term is ambiguous, the single word "ton" being variously used for short, long, and metric tons.

<span class="mw-page-title-main">Barrel (unit)</span> Series of units for volume measurement

A barrel is one of several units of volume applied in various contexts; there are dry barrels, fluid barrels, oil barrels, and so forth. For historical reasons the volumes of some barrel units are roughly double the volumes of others; volumes in common use range approximately from 100 to 200 litres. In many connections the term drum is used almost interchangeably with barrel.

The tonne of oil equivalent (toe) is a unit of energy defined as the amount of energy released by burning one tonne of crude oil. It is approximately 42 gigajoules or 11.630 megawatt-hours, although as different crude oils have different calorific values, the exact value is defined by convention; several slightly different definitions exist. The toe is sometimes used for large amounts of energy.

A system of units of measurement, also known as a system of units or system of measurement, is a collection of units of measurement and rules relating them to each other. Systems of measurement have historically been important, regulated and defined for the purposes of science and commerce. Instances in use include the International System of Units or SI, the British imperial system, and the United States customary system.

<span class="mw-page-title-main">Deadweight tonnage</span> Measure of how much weight a ship can carry

Deadweight tonnage or tons deadweight (DWT) is a measure of how much weight a ship can carry. It is the sum of the weights of cargo, fuel, fresh water, ballast water, provisions, passengers, and crew.

Specific energy or massic energy is energy per unit mass. It is also sometimes called gravimetric energy density, which is not to be confused with energy density, which is defined as energy per unit volume. It is used to quantify, for example, stored heat and other thermodynamic properties of substances such as specific internal energy, specific enthalpy, specific Gibbs free energy, and specific Helmholtz free energy. It may also be used for the kinetic energy or potential energy of a body. Specific energy is an intensive property, whereas energy and mass are extensive properties.

<span class="mw-page-title-main">Comparison of the imperial and US customary measurement systems</span>

Both the British imperial measurement system and United States customary systems of measurement derive from earlier English unit systems used prior to 1824 that were the result of a combination of the local Anglo-Saxon units inherited from Germanic tribes and Roman units.

Energy is defined via work, so the SI unit of energy is the same as the unit of work – the joule (J), named in honour of James Prescott Joule and his experiments on the mechanical equivalent of heat. In slightly more fundamental terms, 1 joule is equal to 1 newton metre and, in terms of SI base units

Builder's Old Measurement is the method used in England from approximately 1650 to 1849 for calculating the cargo capacity of a ship. It is a volumetric measurement of cubic capacity. It estimated the tonnage of a ship based on length and maximum beam. It is expressed in "tons burden", and abbreviated "tons bm".

<span class="mw-page-title-main">Displacement (ship)</span> Ships weight

The displacement or displacement tonnage of a ship is its weight. As the term indicates, it is measured indirectly, using Archimedes' principle, by first calculating the volume of water displaced by the ship, then converting that value into weight. Traditionally, various measurement rules have been in use, giving various measures in long tons. Today, tonnes are more commonly used.

Ship measurements consist of a multitude of terms and definitions specifically related to ships and measuring or defining their characteristics.

<span class="mw-page-title-main">Imperial and US customary measurement systems</span> English (pre 1824), Imperial (post 1824) and US Customary (post 1776) units of measure

The imperial and US customary measurement systems are both derived from an earlier English system of measurement which in turn can be traced back to Ancient Roman units of measurement, and Carolingian and Saxon units of measure.

The quarter was used as the name of several distinct English units based on ¼ sizes of some base unit.


  1. The "pound" used in this article is the avoirdupois pound. Its mass is defined as exactly 0.45359237 kg
  1. "Naval Architecture for All". United States Bureau of Transportation Statistics. Archived from the original on October 10, 2008. 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." This is the weight of 35 cubic feet of Sea Water at a specific gravity of 1.025, compared to Fresh Water, specific gravity of 1.000 usually measured at 60 degrees F. Handy numbers: 35, 36, 37, number of Cubic Feet per Salt Water, Fresh Water and Lube Oil.
  2. "Definitions, Tonnages and Equivalents". Military Sealift Fleet Support Command. Archived from the original on 2013-05-16. Retrieved 2012-12-12.
  3. "General Tables of Units of Measurement". NIST. April 19, 2006 [November 11, 2000]. Archived from the original on 2011-12-10. Retrieved 2013-07-01.
  4. "NIST Handbook 44 Specifications: Handbook 44 – 2023 Appendix C – General Tables of Units of Measurement" (PDF). November 18, 2022. p. C-7. Retrieved May 9, 2023. 20 hundredweights = 1 ton
  5. "Meaning of short ton in English". Cambridge Dictionary. Retrieved May 26, 2023.
  6. 1 2 Le Système international d’unités [The International System of Units](PDF) (in French and English) (9th ed.), International Bureau of Weights and Measures, 2019, ISBN   978-92-822-2272-0
  7. Chris Evans, Göran Rydén, Baltic iron in the Atlantic world in the eighteenth century, p.257, Brill 2007 ISBN   90-04-16153-8
  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. "tonne" . Oxford English Dictionary (Online ed.). Oxford University Press.(Subscription or participating institution membership required.)
  10. "Weights and Measures Act 1985" (PDF). Her Majesty's Stationery Office. 1985-10-30. Archived (PDF) from the original on 2009-12-08. Retrieved 2010-02-03.
  11. "Weights and Measures Act: Canadian units of measure, Schedule II (Section 4)". Department of Justice. Archived from the original on 2011-08-11. Retrieved 2011-07-06.
  12. Fenna, Donald (2002). A Dictionary of Weights, Measures, and Units. Oxford: Oxford University Press. assay ton. ISBN   9780198605225.
  13. Definitions of 2,000, 2,240, 2,352, and 2,400 lb are included in citations listed in the Oxford English Dictionary, 2nd ed. OED cites an 1858 dictionary of trade products "the legal ton by weight is usually 20 cwt".
  14. DesVergers, Jake. "Rules of the Road: Tricky tonnage measurement not about weight". The Triton. Retrieved 2021-04-23.
  15. Displacement ton Dictionary of international trade retrieved 22July2010
  16. A Dictionary of Weights, Measures, and Units, Donald Fenna, 2002 ISBN   0-19-860522-6
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  21. Panama Canal Tolls Archived 2008-09-16 at the Wayback Machine , Panama Canal Authority. Retrieved 10 May 2006.
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  23. "GC(42)/INF/3 - Measures to Strengthen Co-operation in Nuclear, Radiation and Waste Safety" (PDF). Archived (PDF) from the original on 11 July 2017. Retrieved 1 May 2018.
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  25. "2014 Key World Energy Statistics" (PDF). IEA. 2014. p. 6. Archived (PDF) from the original on 5 April 2015.
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  33. Merriam-Webster's English Dictionary defines ton as: "a great quantity".
  34. Colin R. Chapman, Weights, Money and Other Measures Used by our Ancestors, p.93, Genealogical Publishing Com, 1996 ISBN   0-8063-1501-6.
  35. MacRae-Hall, John (2011). A Deniable Asset. iUniverse. p. 85. ISBN   9781450280808.
  36. The Oxford English Dictionary 2nd ed. lists colloquial use of "ton" from 1946 for £100, and later 100 mph, and for 100 in general.
  37. Bruce Donaldson, Dutch: A Comprehensive Grammar, page 357, Routledge, 2008 ISBN   1134082363 .
  38. A Description of Holland, page 267, J. and P. Knapton, 1743.