Tonne

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For the units of mass, force, and other quantities in general, see Ton.

A tonne (symbol t), sometimes referred to as a metric tonne, is a measurement of weight. It is not an SI unit but is accepted for use with the SI. Though the spelling tonne predates the introduction of the SI system in 1960 it is now used as the standard spelling for the metric weight measurement in English. The similar English units are spelled ton in English.

1 Definition
2 Multiples
3 Origin
4 Conversions
5 Explanation
6 Use of mass as proxy for energy
7 See also
8 References

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Definition

1 tonne = 1000 kilograms.

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Multiples

Multiple	Name	Symbol
10⁰	tonne	t
10¹	decatonne	dt
10²	hectotonne	ht
10³	kilotonne	kt
10⁶	megatonne	Mt
10⁹	gigatonne	Gt
10¹²	teratonne	Tt
10¹⁵	petatonne	Pt
10¹⁸	exatonne	Et
10²¹	zettatonne	Zt
10²⁴	yottatonne	Yt

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Origin

The spelling tonne is from French. In old English the spelling was tunne. The various spellings and meanings (tonne, ton, tun) derive from the late Latin tunna, "cask" - a full cask about a metre high could easily weigh a tonne. It may also be of Celtic origin.

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Conversions

One tonne is equivalent to:

1 megagram (exactly). Symbol Mg. This is the SI term
1000/0.45359237 pounds (exactly) ~ 2205 pounds

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Explanation

The official symbol is t. T and mT and mt (especially in the combination mmt for "million metric tons") are also sometimes 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 1000th.)

In France and the English-speaking countries that are predominantly metric, the spelling tonne is widespread. However, in Britain, the ton used prior to metrication was the long ton of 2240 pounds (approximately 1016 kg). This is so close to the tonne that many 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. [1] In the US an unqualified mention of a "ton" almost invariably refers to a short ton.

Like grams and kilograms, tonnes gave rise to a (now obsolete) force unit of the same name: 1 tonne-force = 9.80665 kilonewtons (kN), a unit also often called simply "tonne" or "metric ton" without identifying it as a unit of force. Note that it is only the tonne as a unit of mass which is accepted for use with SI; the tonne-force or metric ton-force is not acceptable for use with SI.

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Use of mass as proxy for energy

However, the tonne of trinitrotoluene (TNT) is used as a proxy for energy. Prefixes are also used e.g. kilotonne, megatonne, gigatonne; especially for expressing nuclear weapon yield, based on a specific combustion energy of TNT of 4.184 MJ/kg (or one calorie—specifically a thermochemical calorie—per milligram). Hence, 1 kt TNT = 4.184 TJ, 1 Mt TNT = 4.184 PJ.

The SI unit of energy is the joule. Assuming that TNT contains 1000 small (thermochemical) calories per gram (4.184 kJ/g), one tonne TNT is more correctly referred to as 4.184 gigajoules. It is usually used to describe the energy of explosions.

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