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:''This article is about the tonne or metric ton. For other tons, see [[ton]]. For the WWII fighter pilot, see [[Wolfgang Tonne]].''

A '''tonne''' ('''t''') or '''metric ton''', also referred to as a '''''metric tonne''''' or '''''tonne métrique''''', is a measurement of mass equal to 1,000 [[kilogram]]s, or 2204.6226 pounds.  It is not an [[SI]] unit but is accepted for use with the SI.<ref>Section 4.1 of [http://www.bipm.org/utils/common/pdf/si_brochure_8_en.pdf The International System of Units (SI)] (PDF), 8th Edition, 2006</ref> The proper SI unit for a tonne would be a "megagram" (Mg, see [[SI prefix]]), but this term is rarely used in practice. Though the spelling ''tonne'' predates the introduction of the SI system in 1960 (it has been used in France for about two and a half centuries, where it comes from), it is now used as the standard spelling for the metric mass measurement in some English-speaking countries. In the United States the correct term is ''metric ton''.<ref name="FR1998">"Metric System of Measurement: Interpretation of the International System of Units for the United States", [[Federal Register]] notice of [[July 28]] [[1998]], 63 F.R. 40333 [http://ts.nist.gov/WeightsAndMeasures/Metric/upload/SIFedReg.pdf] (PDF)</ref> The comparable [[Imperial unit|imperial]] and [[United States customary units|US customary]] units are spelled '''ton''' in English.

In the [[United States|U.S.]] this unit was defined in 1866<ref> Act of [[July 28]] [[1866]], codified in 15 U.S.C. §205 [http://fatty.law.cornell.edu/uscode/html/uscode15/usc_sec_15_00000205----000-notes.html]</ref> as a ''millier'' or a ''tonneau'' (both French words). This measure was used in Europe centuries earlier; the ''millier'' was formerly 1000 ''[[Pound (mass)#French livre|livres]]'' (489.5 kg)<ref>[http://sizes.com/units/millier.htm Sizes.com: millier]</ref> and the ''tonneau'' was a wine cask size equivalent to the [[Tun (unit)|tun]], containing ~904.8 L<ref>[http://sizes.com/units/charts/UTBLFrance_misc_liqcap.htm Sizes.com: France, selected areas - pre-metric units of liquid capacity]</ref>. However, neither of these latter words is in use in the U.S. and though they  still appear in the statute, they have been declared obsolete by [[National Institute of Standards and Technology|NIST]].<ref name="FR1998"/>

==Definition==
1 tonne is defined as '''1000 kilograms''' or '''1 megagram''' ([[SI prefix|Mg]]) (kilokilogram is incorrect per CIPM, 1967: Recommendation 2<ref>[http://www.bipm.org/en/CIPM/db/1967/2/ Decimal multiples and submultiples of the unit of mass , BIPM - CIPM, 1967]</ref>)

==Multiples ==<!-- This section is linked from [[Water]] -->
{|class="wikitable"
! Multiple        !! Name       !! Symbol
|rowspan="12"|
! Multiple        !! Name       !! Symbol
|rowspan="12"|
! Multiple        !! Name       !! Symbol
|rowspan="12"|
! Multiple        !! Name       !! Symbol
|-
|10<sup>0</sup>   || '''tonne'''|| t
|10<sup>6</sup>   || megagram   || Mg
|10<sup>0</sup>   || '''tonne'''|| t
|10<sup>6</sup>   || megagram   || Mg
|-
|10<sup>1</sup>   || decatonne  || dat
|10<sup>7</sup>   || ''<font color="orange">(none)</font>'' || ''<font color="orange">(none)</font>''
|10<sup>–1</sup> || decitonne   || dt
|10<sup>5</sup>   || ''<font color="orange">(none)</font>'' || ''<font color="orange">(none)</font>''
|-
|10<sup>2</sup>   || hectotonne || ht
|10<sup>8</sup>   || ''<font color="orange">(none)</font>'' || ''<font color="orange">(none)</font>''
|10<sup>–2</sup> || centitonne  || ct
|10<sup>4</sup>   || ''<font color="orange">(none)</font>'' || ''<font color="orange">(none)</font>''
|-
|10<sup>3</sup>   || kilotonne    || kt
|10<sup>9</sup>   || gigagram    || Gg
|10<sup>–3</sup> || millitonne   || mt
|10<sup>3</sup>   || kilogram    || kg
|-
|10<sup>6</sup>   || megatonne  || Mt
|10<sup>12</sup>  || teragram    || Tg
|10<sup>–6</sup>  || microtonne || µt
|10<sup>0</sup>      || gram    || g
|-
|10<sup>9</sup>   || gigatonne  || Gt
|10<sup>15</sup>      || petagram    || Pg
|10<sup>–9</sup>  || nanotonne  || nt
|10<sup>-3</sup>      || milligram    || mg
|-
|10<sup>12</sup>  || teratonne  || Tt
|10<sup>18</sup>      || exagram    || Eg
|10<sup>–12</sup> || picotonne  || pt
|10<sup>-6</sup>    || microgram   ||  μg
|-
|10<sup>15</sup>  || petatonne  || Pt
|10<sup>21</sup>      || zettagram    || Zg
|10<sup>–15</sup> || femtotonne || ft
|10<sup>-9</sup>      || nanogram    || ng
|-
|10<sup>18</sup>  || exatonne   || Et
|10<sup>24</sup>      || yottagram    || Yg
|10<sup>–18</sup> || attotonne  || at
|10<sup>-12</sup>      || picogram    || pg
|-
|10<sup>21</sup>  || zettatonne || Zt
|10<sup>27</sup> || ''<font color="orange">(none)</font>'' || ''<font color="orange">(none)</font>''
|10<sup>–21</sup> || zeptotonne || zt
|10<sup>-15</sup>  || femtogram    || fg
|-
|10<sup>24</sup>  || yottatonne || Yt
|10<sup>30</sup>|| ''<font color="orange">(none)</font>'' || ''<font color="orange">(none)</font>''
|10<sup>–24</sup> || yoctotonne || yt
|10<sup>-18</sup>      || attogram    || ag
|-
|-
|}

The fractional multipliers are rarely used with the tonne unit basis, as the gram is both more fundamental and uses more familiar scaling factors.  Hence 10 kilograms is more common than 10 millitonnes, or 5 ng rather than 5 ft.

==Origin==
The spelling ''tonne'' is from [[Gallic]] and [[French language|French]]. The term applied to the barrel of the largest size. In [[Old English]] the spelling was tunne, "[[Barrel|cask]]" - a full cask about a metre high could easily weigh a tonne. The antiquated British wine cask volume measurement [[Tun (unit)|tun]] is close to a metric tonne in weight as it defines about 954 litres which for many commonly used liquids approximates to as many kilograms.

==Conversions==
One tonne is equivalent to:
*One megagram (exactly); symbol [[SI prefix|Mg]]
**This is the official SI term, but not generally used in industry, in shipping nor {{Wdy|colloquial}}ly
*1000/0.45359237 [[Pound (mass)|pounds]] (exactly by definition), giving approximately
**2204.622 621 848 775 807 lb (to 19 [[significant digit]]s)
**2204.622 622 lb (to ten significant digits)—an easy-to-remember figure
**2205 lb (to four significant digits)
*98.44% of a [[long ton]]
**One long ton (2240 lb) is 101.605% of a tonne
*110.23% of a [[short ton]]
**One short ton (2000 lb) is 90.72% of a tonne

==Explanation==
The official symbol is '''t'''. '''T''' and '''mT''' and '''mt''' (especially in the combination '''mmt''' for "million metric tons" compare to Mt for megatonne) 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 (unit)|tesla]] and m is SI prefix 'milli', meaning 1000th (though in practice fractional prefixes aren't generally used with the tonne). '''Te''' is also sometimes used, particularly in the nuclear industry.

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&nbsp;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.<ref>[http://lamar.colostate.edu/~hillger/laws/63fr40333.pdf Metric System of Measurement: Interpretation of the International System of Units for the United States] (PDF). See corrections in the Errata section of [http://lamar.colostate.edu/~hillger/laws/nist-interpretation.html].</ref> In the U.S. an unqualified mention of a "ton" almost invariably refers to a [[short ton]] of 2000 lb (about 907 kg).

Like grams and kilograms, tonnes gave rise to a (now obsolete) force unit of the same name:  1 tonne-force = 9.80665 [[newton|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.

==Use of mass as proxy for energy==<!-- This section is linked from [[Impact event]] -->
{{main|TNT equivalent}}

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 [[Fuel value|specific combustion energy]] of TNT of 4.184&#160;[[megajoule|MJ]]/[[kilogram|kg]] (or one [[calorie]]&mdash;specifically a ''thermochemical'' calorie&mdash;per [[milligram]]).  Hence, 1 [[kiloton|kt]] TNT = 4.184&#160;[[Terajoule|TJ]], 1&#160;[[megaton|Mt]] TNT = 4.184&#160;[[Petajoule|PJ]].

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

==Derived units==
'''metric ton unit'''<br>
A metric ton unit (MTU) can mean 10 kg (22.046226 pounds) 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.<ref>[http://www.emis.platts.com/thezone/guides/platts/metals/conversion.html Platt's Metals Guide to Specifications]</ref><ref>[http://www.unc.edu/~rowlett/units/dictM.html How Many? A Dictionary of Units of Measurement]</ref>

If the metal is uranium, the acronym 'MTU' is sometimes considered to be 'metric ton of uranium' i.e. 1000 kg.<ref>[http://www-pub.iaea.org/MTCD/publications/PDF/rwmp-3/REFERENCE.pdf Reference.Pdf<!-- Bot generated title -->]</ref><ref>"[http://www.hanford.gov/rl/uploadfiles/ea/ea1319/ea1319.html Glossary]". (June 2000). ''Disposition of Surplus Hanford Site Uranium, Hanford Site, Richland, Washington''. US Department of Energy.</ref><ref>"[http://www.y12.doe.gov/library/acronyms/letter.php?index=M Acronyms]". Y-12 National Security Complex.</ref><ref>[http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr0544/r4/ NRC Collection of Abbreviations (NUREG-0544, Rev. 4), UNITED STATES NUCLEAR REGULATORY COMMISSION]</ref>

==See also==
{|
|-valign=top
|
* [[International System of Units]]
* [[Metre-tonne-second system of units]],<br>a system of measurement that<br> uses the tonne as a base [[unit of measurement|unit]]
* Units using the tonne
** [[ton of oil equivalent]]
** [[GTOE]]
| width=40 |
|
* Other [[ton]]s
** [[short ton]] (S/T)
** [[long ton]] (L/T)
** [[tonnage]]
** [[ton (volume)]]
* [[Conversion of units]]
* [[Orders of magnitude (mass)]]
|}

==References==
{{Reflist}}
*NIST Special Publication 811, [http://physics.nist.gov/Pubs/SP811/ ''Guide for the Use of the International System of Units (SI)'']

[[Category:Units of mass]]
[[Category:Non-SI metric units]]