Tonne

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

The tonne (unit symbol t) or metric ton (US),^[1] often written pleonastically as metric tonne, is a unit of mass equal to 1,000 kg (2,204.62 lb). It is sometimes abbreviated mt in the United States,^[2] although this conflicts with other SI symbols. The tonne is not a unit in the International System of Units (SI), but is accepted for use with the SI.^[3][4] In SI units and prefixes, the tonne is a megagram (Mg).

Unit Symbol

The unit symbol for the tonne is t. T and mT and mt (especially in the combination mmt for million metric tons compare to Mt for megatonne) are also occasionally used, but all of these are deprecated since they conflict with internationally agreed SI symbols. (T is the SI symbol for the tesla and m is SI prefix 'milli', meaning 0.001.) Te is also sometimes used, particularly in the offshore and nuclear industries.

Origin and spelling

In France and the English-speaking countries that are predominantly metric, the spelling tonne is widespread. This is generally true in Britain; however, the ton used prior to metrication was the long ton of 2,240 pounds (1,016 kg) and this is so close to the tonne that some people draw little distinction and continue to use the old spelling. For example, even the Guinness Book of World Records accepts metrication without marking this by changing the spelling. For the United States, metric ton is the name for this unit used and recommended by NIST.^[5] In the US an unqualified mention of a ton almost invariably refers to a short ton of 2,000 pounds (907 kg).

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.^[6] A full tun, standing about a metre high, could easily weigh a tonne. The old English wine cask volume measurement known as a tun is close to a metric tonne in weight as it defines about 954 litres which for many commonly used liquids (aqueous solutions) approximates to as many kilograms.

The spelling tonne pre-dates the introduction of the SI in 1960; it has been used with this meaning in France since 1842,^[7] 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.^{[8][9][10][11]} In the United States, the unit was originally referred to using the French words millier or tonneau,^[12] but these terms are now obsolete.^[1] The Imperial and US customary units comparable to the tonne are both spelled ton in English, though they differ in mass. Pronunciation of tonne (the word used in the United Kingdom) and ton is usually identical.

Conversions

One tonne is equivalent to:

• One megagram (exactly);
  • megagram is the official SI term, but generally not used in industry or shipping, nor colloquially
• ¹⁰⁰⁰⁄_{0.453 592 37} pounds (exactly by definition),^[13] giving approximately
  • 2205 lb (to four significant digits)
• 98.42% of a long ton
  • One long ton (2,240 lb) is 101.605% of a tonne
• 110.23% of a short ton
  • One short ton (2,000 lb) is 90.72% of a tonne

Derived units

Tonnes			Grams
Multiple	Name	Symbol	Multiple	Name	Symbol
100	tonne	t	106	megagram	Mg
103	kilotonne	kt	109	gigagram	Gg
106	megatonne	Mt	1012	teragram	Tg
109	gigatonne	Gt	1015	petagram	Pg
1012	teratonne	Tt	1018	exagram	Eg
1015	petatonne	Pt	1021	zettagram	Zg
1018	exatonne	Et	1024	yottagram	Yg

Alternate usage

A metric ton unit (MTU) can mean 10 kilograms (22 lb) within metal (e.g., tungsten, manganese) trading, particularly within the USA. It traditionally referred to a metric ton of ore containing 1% (i.e. 10 kg) of metal.^[14][15]

In the case of uranium, the acronym MTU is sometimes considered to be metric ton of uranium, meaning 1,000 kg.^{[16][17][18][19]}

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

• Ton
  • Short ton
  • Long ton
  • Tonnage
  • Ton (volume)

• Metre-tonne-second system of units
• Tonne of oil equivalent
• Orders of magnitude (mass)

References

1. ^ ^{a b} "Metric System of Measurement: Interpretation of the International System of Units for the United States" (PDF). Federal Register 63 (144): 40333–40340. July 28, 1998. 63 FR 40333. http://ts.nist.gov/WeightsAndMeasures/Metric/upload/SIFedReg.pdf. 
2. ^ NASA Human Spaceflight Commission Final Report: Seeking a Human Spaceflight Program Worthy of a Great Nation, October 2009, Review of U.S. Human Spaceflight Plans Committee, p. 65-66.
3. ^ The International System of Units (SI) (PDF), 8th Edition, 2006, Section 4.1
4. ^ Table 6. BIPM. Retrieved on 2011-07-10.
5. ^ Metric System of Measurement: Interpretation of the International System of Units for the United States (PDF). See corrections in the Errata section of [1].
6. ^ Harper, Douglas. "tonne". Online Etymology Dictionary. http://www.etymonline.com/index.php?term=tonne. 
7. ^ TLF French dictionary
8. ^ "Guidance Note on the use of Metric Units of Measurement by the Public Sector". National Measurement Office. 2007. http://www.nmo.bis.gov.uk/Docs/Legislation/Units%20of%20Measurement/Gnotes%20for%20public%20sector%20on%20use%20of%20metric.pdf. Retrieved 2010-02-13.  "Tonne" is listed under "The Principal Metric Units of Measurement" on p. 7.
9. ^ "National Measurement Regulations 1999 |". Australian Government. 1999. http://www.comlaw.gov.au/ComLaw/Legislation/LegislativeInstrumentCompilation1.nsf/framelodgmentattachments/35F21696B4C9E27CCA2575EC001FA5D1. 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.
10. ^ "Appendix 4: Units of Measurement and Conversion Factors". MAF (Ministry of Agriculture and Forestry (New Zealand)). http://www.maf.govt.nz/statistics/forestry/annual/nzstats2000/appendix/append4.htm. Retrieved 2010-02-13. 
11. ^ "Canada Gazette". Government of Canada. 1998-2007. http://www.gazette.gc.ca/archives/p2/1999/1999-11-10/html/sor-dors430-eng.html. 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..." 
12. ^ Act of July 28, 1866, codified in 15 U.S.C. § 205
13. ^ Barbrow, L.E.; Judson, L.V. (1976). Weights and measures standards of the United States – A brief history. http://physics.nist.gov/Pubs/SP447/contents.html. 
14. ^ Platt's Metals Guide to Specifications
15. ^ How Many? A Dictionary of Units of Measurement. Unc.edu. Retrieved on 2011-07-10.
16. ^ Reference.Pdf. (PDF) . Retrieved on 2011-07-10.
17. ^ "Glossary". (June 2000). Disposition of Surplus Hanford Site Uranium, Hanford Site, Richland, Washington. US Department of Energy.
18. ^ "Acronyms". Y-12 National Security Complex.
19. ^ NRC Collection of Abbreviations (NUREG-0544, Rev. 4), United States Nuclear Regulatory Commission. Nrc.gov (2011-03-13). Retrieved on 2011-07-10.

• NIST Special Publication 811, Guide for the Use of the International System of Units (SI)