Ton

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 mass. Its original use as a measurement of volume has continued in the capacity of cargo ships and in terms such as the freight ton. Recent specialised uses include the ton as a measure of energy and for truck classification. It is also a colloquial term.

Not to be confused with the Tonne (t) unit of mass accepted in the SI system or with Tonnage. For other uses, see Ton (disambiguation).
ton
General information
Unit system
Unit ofMass
Symbolt
Conversions
1 t in ...... is equal to ...
   SI derived unit   1016.0469 kg (long)
   SI derived unit   907.18474 kg (short)

In the United Kingdom, the (Imperial) ton is a statute measure, defined as 2,240 lb (1,016 kg).[lower-alpha 1][1] In the United States and Canada,[2] a ton is defined to be 2,000 pounds (907.18474 kg). Where confusion is possible, the 2240 lb ton is called "long ton" and the 2000 lb ton "short ton"; the tonne is distinguished by its spelling, but usually pronounced the same as ton, hence the US term "metric ton". In the UK the final "e" of "tonne" can also be pronounced (/ˈtʌni/),[3] or "metric ton" when it is necessary to make the distinction.

Where precision is required the correct term must be used, but for many purposes this is not necessary: the metric and long tons differ by only 1.6%, and the short ton is within 11% of both. The ton (any definition) is the heaviest unit of weight typically used in colloquial speech.

The term "ton" is also used to refer to a number of units of volume, ranging from 35 to 100 cubic feet (0.99 to 2.83 m3) in capacity. It can also be used as a unit of energy, or in refrigeration as a unit of power, sometimes called a ton of refrigeration. It is also used informally to mean a large amount of something, material or not.

History

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.[4]

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,[5] weight ton "ton" (UK)[lower-alpha 2] 2,240 lb (1,016.0469 kg) Used in countries such as the United Kingdom and Commonwealth of Nations that formerly used, or still use the Imperial system
short ton[6] "ton" (US) 2,000 lb (907.18474 kg) Used in the U.S., and formerly in Canada
tonne;[7] correctly called a Megagram "tonne";[lower-alpha 2] "metric ton"

(mainly UK)

 1,000 kg (2,204.6226 lb) Defined in the International System of Units.

Used worldwide.

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

1.58% less than the long ton.

ton shortweight[lower-alpha 3] 2240 lb Used in the iron industry in the 17th and 18th centuries.
ton longweight[lower-alpha 3] 2400 lb[lower-alpha 4] Used in the iron industry in the 17th and 18th centuries.
  1. The "pound" used in this article is the avoirdupois pound. Its mass is defined as exactly 0.45359237 kg
  2. In the UK, the words "ton" and "tonne" are usually pronounced the same way, /tʌn/. As the imperial ton and the (metric) tonne only differ by 2%, ambiguity is not typically a problem; where accuracy is required in speech, "long ton" or exaggerated pronunciation of "tonne" emphasising the "e", /ˈtʌni/, are used.[3]
  3. 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.[8]
  4. 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 unfair in favour of the mine owners.[9]

Other units of mass/weight
  • 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 (2,240 pounds (1,016 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.
  • Harbour ton, used in South Africa in the 20th century, was equivalent to 2000 pounds or one short ton.

Both the long ton and the short ton are 20 hundredweight, the long hundredweight and the short hundredweight being 112 and 100 pounds respectively. Before the twentieth 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). In the nineteenth century in different parts of Britain, definitions of 2240, 2352, and 2400 lb were used, with 2000 lb for explosives; the legal ton was usually 2240 lb.[10]

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 ​29 1⁄6 grams while a long assay ton is ​32 2⁄3 gram. 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, 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.

Subdivisions

In the Imperial units system, the imperial (long) ton is equivalent to 20 hundredweight, a hundredweight being eight stone, and a stone weighing 14 pounds.

Units of volume
See also: Tonnage

The displacement, essentially the weight, of a ship is traditionally expressed in long tons. 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.[11] 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).[12] 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 sometimes abbreviated as "MTON". It is used to determine the amount of money to be charged as "Freight" in 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.[13][14][15][16] 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" 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 may cause it to be confused with the megatonne.

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.[17]

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),[18] 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
Main article: TNT equivalent
  • 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 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 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).[19][20] 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).[21]

Unit conversion factors for toe
toeMWhGJGcalmillion Btutce
111.6341.8681039.68320721.42857143
Source: conversion factors as used by the IEA[22]

Other sources convert 1 toe into 1.28 tonne of coal equivalent (tce).[23] 1 toe is also standardized as 7.33 barrel of oil equivalent (boe).[24]

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
tceMWhGJGcalmillion Btutoe
18.14129.3076727.7782450.7
Source: conversion factors as used by the IEA[22]

Refrigeration
Main article: Ton of refrigeration

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.

  • 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)."[26] 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 short ton (0.893 long tons; 0.907 t) of ice per day.
  • A less common usage is the power required to cool 1 long ton (2,240 lb or 1,016 kg = 1 long ton or 1.120 short tons or 1.016 t) of water by 1 °F (0.56 °C) every 10 minutes = 13,440 BTU/h (3,939 W).[27][28]

A refrigeration ton should be regarded as power produced by a chiller when operating in standard AHRI 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 18.3 °C) which can show more favorable data, which are not valid when making performance comparisons among units unless conversion rates are applied.

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, "I have a ton of homework to do this weekend."
  • 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 any other countable figure.[29][30][31]
  • In Dutch, when talking about money a ton is used to indicate 100,000. For example a house costing 2 ton would cost 200,000 euros.[32] This convention has been in use since at least the 18th century.[33]
  • In Finnish, tonni is often used as a synonym for 1000, especially when referring to money. For example, tonnin seteli was a 1000-mark banknote, and a popular TV show was called Kymppitonni ("ten tons" = 10,000 marks).

See also

References
    1. "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.
    2. "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.
    3. "tonne". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
    4. "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.
    5. "Archived copy". Archived from the original on 2013-05-16. Retrieved 2012-12-12.CS1 maint: archived copy as title (link)
    6. "Archived copy". Archived from the original on 2011-12-10. Retrieved 2013-07-01.CS1 maint: archived copy as title (link)
    7. "Archived copy" (PDF). Archived (PDF) from the original on 2013-11-05. Retrieved 2012-10-17.CS1 maint: archived copy as title (link)
    8. Chris Evans, Göran Rydén, Baltic iron in the Atlantic world in the eighteenth century, p.257, Brill 2007 ISBN 90-04-16153-8
    9. "Report of the select committee on mines", Reports from Committees 1866, vol.9, pp.134-136, London: House of Commons, 23 July 1866
    10. Definitions of 2000, 2240, 2352, and 2400 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".
    11. Displacement ton Dictionary of international trade retrieved 22July2010
    12. A Dictionary of Weights, Measures, and Units, Donald Fenna, 2002 ISBN 0-19-860522-6
    13. "MSC 2003 in Review - Financial and Statistical Review". Msc.navy.mil. 2003-09-30. Archived from the original on 2011-07-22. Retrieved 2010-07-31.
    14. "Liner Ocean Transportation Program Stabilized Breakbulk/Dry Cargo and Container Billing Rates" (PDF). Military Surface Deployment and Distribution Command. 2018.
    15. "182 F.2d 916". Bulk.resource.org. Archived from the original on 2011-07-27. Retrieved 2010-07-31.
    16. "Pos Ttariff General Definitions". Stocktonport.com. Archived from the original on 2011-07-16. Retrieved 2010-07-31.
    17. Panama Canal Tolls Archived 2008-09-16 at the Wayback Machine, Panama Canal Authority. Retrieved 10 May 2006.
    18. "NIST: Units and Systems of Measurement Their Origin, Development, and Present Status". nist.gov. Archived from the original on 16 June 2016. Retrieved 1 May 2018.
    19. "GC(42)/INF/3 - Measures to Strengthen Co-operation in Nuclear, Radiation and Waste Safety" (PDF). iaea.org. Archived (PDF) from the original on 11 July 2017. Retrieved 1 May 2018.
    20. Radioactive residues of the Cold War period Archived 2005-10-16 at the Wayback Machine
    21. "2014 Key World Energy Statistics" (PDF). iea.org/publications/freepublications/. IEA. 2014. p. 6. Archived (PDF) from the original on 5 April 2015.
    22. "IEA – Unit Converter". International Energy Agency. Archived from the original on 2 May 2015. Retrieved 5 May 2015.
    23. Goldemberg, José; Lucon, Oswaldo (1 May 2018). "Energy, Environment and Development". Earthscan. Retrieved 1 May 2018 – via Google Books.
    24. "Conversion factors". OPEC Annual Statistical Bulletin 2014. Archived from the original on 2016-10-11.
    25. "Coal Conversion Statistics". World Coal Association. Archived from the original on 16 May 2015. Retrieved 5 May 2015.
    26. Marks' Standard handbook for Mechanical Engineers, 8th Ed., McGraw Hill, p. 19–3
    27. "ton (of refrigeration)". Sizes.com. Archived from the original on 2006-10-20. Retrieved 2006-09-01. External link in |work= (help)
    28. Gérard P. Michon. "Measurements and Units". Archived from the original on 2010-03-28. Retrieved 2006-09-01.
    29. Colin R. Chapman, Weights, Money and Other Measures Used by our Ancestors, p.93, Genealogical Publishing Com, 1996 ISBN 0-8063-1501-6.
    30. MacRae-Hall, John (2011). A Deniable Asset. iUniverse. p. 85. ISBN 9781450280808.
    31. The Oxford English Dictionary 2nd ed. lists colloquial use of "ton" from 1946 for £100, and later 100 mph, and for 100 in general.
    32. Bruce Donaldson, Dutch: A Comprehensive Grammar, page 357, Routledge, 2008 ISBN 1134082363 .
    33. A Description of Holland, page 267, J. and P. Knapton, 1743.
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