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This article is about the metric unit of mass. For other ton units, see Ton. For other uses, see Tonne (disambiguation).

The tonne (Listeni/tʌn/) (British and SI; SI symbol: t) or metric ton is a non-SI metric unit of mass equal to 1000 kilograms;[1][2][3][4] it is thus equivalent to one megagram (Mg). 1,000 kilograms is equivalent to approximately 2,204.6 pounds,[5] 1.10 tons (US) or 0.984 tons (imperial). Although not part of the SI per se, the tonne is "accepted for use with" SI units and prefixes by the CIPM, along with several other units like the bar, litre and day.

Symbol and abbreviations

The SI symbol for the tonne is "t", adopted at the same time as the unit itself in 1879.[2] Its use is also official within the United States, having been adopted by the US National Institute of Standards and Technology.[6] It is a symbol, not an abbreviation, and should not be followed by a period. Informal and non-approved symbols or abbreviations include "T", "mT", "MT", "mt",[7] and "Te" (particularly in the offshore and nuclear industries).[citation needed] Some of these are actually SI symbols for other units: "T" is the SI symbol for the tesla and "Mt" is the SI symbol for megatonne (equivalent to one teragram); if describing TNT equivalent units of energy, this is equivalent to 4.184 petajoules.

Origin and spelling

In French and all English-speaking countries that are predominantly metric, tonne is the correct spelling in writing. It is usually pronounced the same as ton /tʌn/, but when it is important to clarify that the metric term is meant, rather than short ton, the final "e" can also be pronounced /ˈtʌnɪ/[8] In Australia, it is also pronounced /tɒn/.[9]

Before metrication in the UK the unit used for most purposes was the Imperial ton of 2,240 pounds avoirdupois (usually referred to as the long ton in the US), equivalent to 1,016 kg, differing by just 1.6% from the tonne. The UK Weights and Measures Act 1985 explicitly excluded from use for trade many units and terms, including the ton and the term "metric tonne".[10] However, for many purposes the Imperial ton and the tonne are so similar that it is not important to distinguish them, even in writing, and the spelling "ton" is still often used where "tonne" is meant. For example, even the Guinness Book of World Records accepts metrication without marking this by changing the spelling[citation needed]. In the United States metric ton is the name for this unit used and recommended by NIST;[6] an unqualified mention of a ton almost invariably refers to a short ton of Script error: No such module "convert"., and tonne is rarely used in speech or writing.

Ton and tonne are both derived from a Germanic word in general use in the North Sea area since the Middle Ages (cf. Old English and Old Frisian tunne, Old High German and Medieval Latin tunna, German and French tonne) to designate a large cask, or tun.[11] A full tun, standing about a metre high, could easily weigh a tonne. An English tun (an old wine cask volume measurement equivalent to 954 litres) of wine weighs roughly a tonne, 954 kg if full of water, a little less for wine.

The spelling tonne pre-dates the introduction of the SI in 1960; it has been used with this meaning in France since 1842,[12] when there were no metric prefixes for multiples of 106 and above, and is now used as the standard spelling for the metric mass measurement in most English-speaking countries.[13][14][15][16] In the United States, the unit was originally referred to using the French words millier or tonneau,[17] but these terms are now obsolete.[3] The Imperial and US customary units comparable to the tonne are both spelled ton in English, though they differ in mass.


One tonne is equivalent to:

  • Metric/SI: 1 megagram (Mg) (by definition). Equal to 1000000Lua error: Unmatched close-bracket at pattern character 67. or 1000Lua error: Unmatched close-bracket at pattern character 67..
    • Megagram, Mg, is the official SI unit. Mg is distinct from mg, milligram.
  • Pounds (lb): Exactly 1000/0.453 592 37 lb (by definition of the pound),[18] or approximately 2204.622622Lua error: Unmatched close-bracket at pattern character 67. (10 s.f.).
  • US/Short tons (ST): Exactly 1/0.907 184 74 short tons, or approximately 1.102311311 ST (10 s.f.).
    • One short ton is exactly 0.90718474Lua error: Unmatched close-bracket at pattern character 67..[19]
  • Imperial/Long tons (LT): Exactly 1/1.016 046 9088 long tons, or approximately 0.9842065276 LT (10 s.f.).
    • One long ton is exactly 1.0160469088Lua error: Unmatched close-bracket at pattern character 67..[19]

Derived units

For multiples of the tonne, it is more usual to speak of thousands or millions of tonnes. Kilotonne, megatonne, and gigatonne are more usually used for the energy of nuclear explosions and other events, often loosely as approximate figures. When used in this context, there is little need to distinguish between metric and other tons, and the unit is spelt either as ton or tonne with the relevant prefix attached.[20]

tonnes Grams Equivalents*
Multiple Name Symbol Multiple Name Symbol tonnes (t) Kilograms (kg) Grams (g) US/Short Tons (ST) Imperial/Long Tons (LT)
100 tonne t 106 megagram Mg 1 t 1,000 kg 1 million g Script error: No such module "convert". ST Script error: No such module "convert". LT
103 kilotonne ktǂ 109 gigagram Gg 1,000 t 1 million kg 1 billion g Script error: No such module "convert". ST Script error: No such module "convert". LT
106 megatonne Mt 1012 teragram Tg 1 million t 1 billion kg 1 trillion g Script error: No such module "convert". million ST Script error: No such module "convert". LT
109 gigatonne Gt 1015 petagram Pg 1 billion t 1 trillion kg 1 quadrillion g Script error: No such module "convert". billion ST Script error: No such module "convert". million LT
1012 teratonne Tt 1018 exagram Eg 1 trillion t 1 quadrillion kg 1 quintillion g Script error: No such module "convert". trillion ST Script error: No such module "convert". billion LT
1015 petatonne Pt 1021 zettagram Zg 1 quadrillion t 1 quintillion kg 1 sextillion g Script error: No such module "convert". quadrillion ST Script error: No such module "convert". trillion LT
1018 exatonne Et 1024 yottagram Yg 1 quintillion t 1 sextillion kg 1 septillion g Script error: No such module "convert". quintillion ST Script error: No such module "convert". quadrillion LT

*The equivalent units columns use the short scale large-number naming system currently used in most English-language countries, e.g. 1 billion = 1,000 million = 1,000,000,000.

Values in the equivalent short and long tons columns are rounded to five significant figures, see Conversions for exact values.

ǂThough non-standard, the symbol "kt" is also sometimes used for knot, a unit of speed for sea-going vessels, and should not be confused with kilotonne.

Alternative usage

A metric ton unit (MTU) can mean Script error: No such module "convert". within metal (e.g. tungsten, manganese) trading, particularly within the US. It traditionally referred to a metric ton of ore containing 1% (i.e. 10 kg) of metal.[21][22]

In the case of uranium, the acronym MTU is sometimes considered to be metric ton of uranium, meaning 1,000 kg.[23][24][25][26]

In the petroleum industry the tonne of oil equivalent (toe) is a unit of energy: the amount of energy released by burning one tonne of crude oil, approximately 42 GJ. There are several slightly different definitions.

A gigatonne of Carbon dioxide equivalent (GtCO2eq) is a unit used by the UN climate change panel, IPCC, to measure the effect of a technology or process on global warming.

Use of mass as proxy for energy

Main article: TNT equivalent

The tonne of trinitrotoluene (TNT) is used as a proxy for energy, usually of explosions (TNT is a common high explosive). Prefixes are used: kiloton(ne), megaton(ne), gigaton(ne), especially for expressing nuclear weapon yield, based on a specific combustion energy of TNT of about 4.2 MJ/kg (or one thermochemical calorie per milligram). Hence, 1 kt TNT = 4.2 TJ, 1 Mt TNT = 4.2 PJ.

The SI unit of energy is the joule. Assuming that a TNT explosion releases 1,000 small (thermochemical) calories per gram (4.2 kJ/g), one tonne of TNT is equivalent to 4.2 gigajoules.

Unit of force

Like the gram and the kilogram, the tonne gave rise to a (now obsolete) force unit of the same name, the tonne-force, equivalent to about 9.8 kilonewtons: a unit also often called simply "tonne" or "metric ton" without identifying it as a unit of force. In contrast to the tonne as a mass unit, the tonne-force or metric ton-force is not acceptable for use with SI, partly because it is not an exact multiple of the SI unit of force, the newton.

See also

Notes and references

  1. ^ Weights and Measures Act 1985. National Archives (London), 2014. Accessed 13 Aug 2014.
  2. ^ a b Table 6. BIPM. Retrieved on 2011-07-10.
  3. ^ a b "Metric System of Measurement: Interpretation of the International System of Units for the United States" (PDF). Federal Register 63 (144): 40338. July 28, 1998. 63 FR 40333. 
  4. ^ The International System of Units (SI) (PDF), 8th Edition, 2006, Section 4.1
  5. ^ United States National Bureau of Standards (1959-06-25). "Notices "Refinement of values for the yard and the pound"" (PDF). Retrieved 2006-08-12. 
  6. ^ a b Metric System of Measurement: Interpretation of the International System of Units for the United States (PDF). See corrections in the Errata section of [1].
  7. ^ Definition of metric ton (MT)
  8. ^ The Oxford English dictionary 2nd ed. lists both /tʌn/ and /ˈtʌnɪ/
  9. ^ Macquarie Dictionary (fifth ed.). Sydney: Macquarie Dictionary Publishers Pty Ltd. 2009. 
  10. ^ A Dictionary of Weights, Measures, and Units, edited by Donald Fenna, Oxford University Press
  11. ^ Harper, Douglas. "tonne". Online Etymology Dictionary. 
  12. ^ TLF French dictionary
  13. ^ "Guidance Note on the use of Metric Units of Measurement by the Public Sector" (PDF). National Measurement Office. 2007. Retrieved 2010-02-13.  "Tonne" is listed under "The Principal Metric Units of Measurement" on p. 7.
  14. ^ "National Measurement Regulations 1999 |". Australian Government. 1999. Retrieved 2010-02-13.  "Tonne" is listed under Schedule 1, Part 3 as a non-SI unit of measurement used with SI units of measurement.
  15. ^ "Appendix 4: Units of Measurement and Conversion Factors". MAF (Ministry of Agriculture and Forestry (New Zealand)). Retrieved 2010-02-13. 
  16. ^ "Canada Gazette". Government of Canada. 1998–2007. Retrieved 2010-02-13. The Corporation shall pay to producers selling and delivering wheat produced in the designated area to the Corporation the following sums certain per tonne basis... 
  17. ^ Act of July 28, 1866, codified in 15 U.S.C. § 205
  18. ^ Barbrow, L.E.; Judson, L.V. (1976). Weights and measures standards of the United States – A brief history. 
  19. ^ a b National Institute of Standards and Technology. Butcher, Tina; Crown, Linda; Harshman, Rick; Williams, Juana, eds. (October 2013). "Appendix C – General Tables of Units of Measurement" (PDF). Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices. NIST Handbook 44 (2014 ed.). Washington, D.C.: U.S. Department of Commerce, Technology Administration, National Institute of Standards and Technology. p. C-13. ISSN 0271-4027. OCLC 58927093. Retrieved 10 December 2013. 
  20. ^ The Oxford English Dictionary 2nd ed. gives both megaton and megatonne and adds "The unit may be calculated in either imperial or metric tons; the form megatonne generally implies the metric unit". The use for energy is the first definition; use for mass or weight is the third definition.
  21. ^ Platt's Metals Guide to Specifications
  22. ^ How Many? A Dictionary of Units of Measurement. Retrieved on 2011-07-10.
  23. ^ Reference.Pdf. (PDF) . Retrieved on 2011-07-10.
  24. ^ "Glossary". (June 2000). Disposition of Surplus Hanford Site Uranium, Hanford Site, Richland, Washington. US Department of Energy.
  25. ^ "Acronyms". Y-12 National Security Complex.
  26. ^ NRC Collection of Abbreviations (NUREG-0544, Rev. 4), United States Nuclear Regulatory Commission. (2011-03-13). Retrieved on 2011-07-10.

External links