TheBIPM symbol for the tonne is t, adopted at the same time as the unit in 1879.[1] Its use is also official for the metric ton in the United States, having been adopted by the United StatesNational Institute of Standards and Technology (NIST).[2][3] It is a symbol, not an abbreviation, and should not be followed by aperiod. Use of lower case is significant, and use of other letter combinations can lead to ambiguity. For example, T, MT, mT, are the SI symbols for thetesla, megatesla, and millitesla, respectively, while Mt and mt are SI-compatible symbols for the megatonne (one teragram) and millitonne (one kilogram). If describingTNT equivalent units of energy, one megatonne of TNT is equivalent to approximately 4.184petajoules.
In English,tonne is an established spelling alternative tometric ton.[4] In American English and British English, tonne is usually pronounced the same as ton (/tʌn/), but the final "e" can also be pronounced, i.e. "tunnie" (/ˈtʌni/).[5] In Australian English, the common and recommended pronunciation is/tɒn/.[6][7] In the United States,metric ton is the name for this unit used and recommended by NIST;[2] an unqualified mention of aton typically refers to ashort ton of 2,000 lb (907.2 kg) and to a lesser extent to along ton of 2,240 lb (1,016 kg), with the termtonne rarely used in speech or writing. Both terms are acceptable inCanadian English.
The spellingtonne pre-dates the introduction of the SI in 1960; it has been used with this meaning in France since 1842,[9] 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 mostEnglish-speaking countries.[10][11][12][13] In the United States, the unit was originally referred to using theFrench wordsmillier ortonneau,[14] but these terms are now obsolete.[15] The British imperial and United States customary units are comparable to thetonne and the spelling ofton in English is the same, though they differ in mass.
As a non-SI unit, the use of SI metric prefixes with the tonne does not fall within the SI standard. 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 inequivalent mass of TNT, 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 spelled either aston ortonne with the relevant prefix attached.[b]
^The equivalent units columns use theshort scale large-number naming system currently used in most English-language countries, e.g. 1 billion = 1000 million =1000000000.
^Though non-standard, the symbol "kt" is also used (instead of the standard symbol "kn") forknot, a unit of speed foraircraft andwatercraft. The standard meaning of the symbol kt is for kilotonne.
Ametric ton unit (mtu) can mean 10 kg (22 lb) within metal trading, particularly within the United States. It traditionally referred to a metric ton of ore containing 1% (i.e. 10 kg) of metal.[20][21]The following excerpt from a mining geology textbook describes its usage in the particular case of tungsten:
Tungsten concentrates are usually traded in metric tonne units (originally designating one tonne of ore containing 1% of WO3, today used to measure WO3 quantities in 10 kg units. One metric tonne unit (mtu) of tungsten (VI) contains 7.93 kilograms of tungsten.
— Walter L Pohl,Economic Geology: Principles and Practices, English edition, 2011, p 183.
In the case ofuranium,MTU is sometimes used in the sense ofmetric ton of uranium (1,000 kg [2,200 lb]).[22][23][24][25]
The SI unit of energy is thejoule. One tonne of TNT is approximately equivalent to 4.2 gigajoules.
In thepetroleum industry, thetonne of oil equivalent (toe) is aunit of energy: the amount of energy released by burning one tonne ofcrude oil, approximately 42 GJ. There are several slightly different definitions. This is ten times as much as a tonne of TNT because atmospheric oxygen is used.
Like thegram and the kilogram, the tonne gave rise to a (now obsolete) force unit of the same name, the tonne-force, equivalent to about 9.8kilonewtons. The unit is 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 is not accepted for use with SI.
^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.
^NISTSpecial Publication 330, 2019 edition states "The name of the unit with symbol t and defined according to 1 t = 103 kg is called 'metric ton' rather than 'tonne.'".
^"National Measurement Regulations 1999 |". Australian Government. 1999. Retrieved2010-02-13. "Tonne" is listed under Schedule 1, Part 3 as a non-SI unit of measurement used with SI units of measurement.
^"Canada Gazette". Government of Canada. 1998–2007. Archived fromthe original on 2011-07-06. Retrieved2010-02-13.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...
^"GlossaryArchived 2010-03-14 at theWayback Machine". (June 2000).Disposition of Surplus Hanford Site Uranium, Hanford Site, Richland, Washington. US Department of Energy.
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