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The tonne ( or ; symbol: t) is a metric unit of mass equal to 1,000 
kilogram The kilogram (also kilogramme) is the base unit of mass Mass is the physical quantity, quantity of ''matter'' in a physical body. It is also a measure (mathematics), measure of the body's ''inertia'', the resistance to acceleration (change ...
s. It is also referred to as a metric ton. It is equivalent to approximately
pounds Pound or Pounds may refer to: Units * Pound (currency), a unit of currency * Pound sterling, the official currency of the United Kingdom * Pound (mass), a unit of mass * Pound (force), a unit of force * Rail pound, in rail profile Symbols * Po ...
; , and 0.984
long ton Long ton, also known as the imperial ton or displacement ton,Dictionary.com - ''"a unit for measuring the displacement of a vessel, equal to a long ton of 2240 pounds (1016 kg) or 35 cu. ft. (1 cu. m) of seawater."'' is the name for the unit calle ...
s (UK). The official SI unit is the megagram (symbol: Mg), a less common way to express the same mass.


Symbol and abbreviations

The
BIPM The International Bureau of Weights and Measures (french: Bureau international des poids et mesures, BIPM) is an intergovernmental organisation An intergovernmental organization (IGO) is an organization composed primarily of sovereign stat ...
symbol for the tonne is t, adopted at the same time as the unit in 1879.Table 6
. BIPM. Retrieved on 2011-07-10.
Its use is also official for the metric ton in the United States, having been adopted by the United States
National Institute of Standards and Technology The National Institute of Standards and Technology (NIST) is a physical sciences Physical science is a branch of natural science that studies abiotic component, non-living systems, in contrast to life science. It in turn has many branches, e ...
(NIST). It is a symbol, not an abbreviation, and should not be followed by a
period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Period, a descriptor for a historical or period drama ...
. Use of
minuscule Letter case (or just case) is the distinction between the Letter (alphabet), letters that are in larger uppercase or capitals (or more formally ''majuscule'') and smaller lowercase (or more formally ''minuscule'') in the written representation ...

minuscule
letter case is significant, and use of other letter combinations can lead to ambiguity. For example, T, MT, mT, Mt and mt are the SI symbols for the tesla, megatesla, millitesla, megatonne (one teragram), and millitonne (one kilogram) respectively. If describing
TNT equivalent TNT equivalent is a convention for expressing energy, typically used to describe the energy released in an explosion. The is a unit of energy Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT ...
units of energy, one megatonne of TNT is equivalent to approximately 4.184
petajoule The joule ( ; symbol: J) is a derived unit of energy In physics, energy is the physical quantity, quantitative physical property, property that must be #Energy transfer, transferred to a physical body, body or physical system to perform W ...
s.


Origin and spelling

In English, ''tonne'' is the established spelling alternative to ''metric ton''. In the US and UK, tonne is usually pronounced the same as ton (), but the final "e" can also be pronounced, i.e. "tunnie" (). In Australia, the common and recommended pronunciation is . In the United States, ''metric ton'' is the name for this unit used and recommended by NIST;Metric System of Measurement: Interpretation of the International System of Units for the United States
(PDF). See corrections in the Errata section o

.
an unqualified mention of a ''ton'' almost invariably refers to a
short ton The short ton (symbol tn) is a mass Mass is the quantity Quantity is a property that can exist as a multitude or magnitude, which illustrate discontinuity and continuity. Quantities can be compared in terms of "more", "less", or "equal ...
of , and ''tonne'' is rarely used in speech or writing. Both terms are acceptable in Canadian usage. ''Ton'' and ''tonne'' are both derived from a
Germanic Germanic may refer to: * Germanic peoples, an ethno-linguistic group identified by their use of the Germanic languages ** List of ancient Germanic peoples and tribes * Germanic languages :* Proto-Germanic language, a reconstructed proto-language of ...

Germanic
word in general use in the
North Sea The North Sea is a sea The sea, connected as the world ocean or simply the ocean The ocean (also the sea or the world ocean) is the body of salt water which covers approximately 71% of the surface of the Earth.
area since the
Middle Ages In the history of Europe The history of Europe concerns itself with the discovery and collection, the study, organization and presentation and the interpretation of past events and affairs of the people of Europe since the beginning of ...
(cf.
Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language English is a West Germanic language of the Indo-European language family The Indo-European languages are a language family A language ...
and
Old Frisian Old Frisian was a West Germanic language spoken between the 8th and 16th centuries in the area between the Rhine ), Surselva Surselva Region is one of the eleven administrative districts Administrative division, administrative unitArticl ...
''tunne'',
Old High German Old High German (OHG, german: Althochdeutsch, German abbr. ) is the earliest stage of the German language German ( Standard High German: , ) is a West Germanic language mainly spoken in Central Europe Central Europe is an area of Euro ...
and
Medieval Latin Medieval Latin was the form of Latin Latin (, or , ) is a classical language A classical language is a language A language is a structured system of communication Communication (from Latin ''communicare'', meaning "to share ...
,
German German(s) may refer to: Common uses * of or related to Germany * Germans, Germanic ethnic group, citizens of Germany or people of German ancestry * For citizens of Germany, see also German nationality law * German language The German la ...

German
and ''tonne'') to designate a large cask, or ''tun''. A full tun, standing about a metre high, could easily weigh a tonne. The spelling ''tonne'' pre-dates the introduction of the SI in 1960; it has been used with this meaning in France since 1842, 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 English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval England, which has eventually become the World language, leading lan ...

English
-speaking countries. In the United States, the unit was originally referred to using the words ''millier'' or ''tonneau'', but these terms are now obsolete. The
Imperial Imperial is that which relates to an empire, emperor, or imperialism. Imperial or The Imperial may also refer to: Places United States * Imperial, California * Imperial, Missouri * Imperial, Nebraska * Imperial, Pennsylvania * Imperial, Texas * ...
and
US customary United States customary units (U.S. customary units) are a Units of measurement, system of measurements commonly used in the United States since it was formalized in 1832. The United States customary system (USCS or USC) developed from English uni ...
units comparable to the tonne are both spelled ''ton'' in English, though they differ in mass.


Conversions

One tonne is equivalent to: *In
kilogram The kilogram (also kilogramme) is the base unit of mass Mass is the physical quantity, quantity of ''matter'' in a physical body. It is also a measure (mathematics), measure of the body's ''inertia'', the resistance to acceleration (change ...
s: by definition. *In
gram The gram (alternative spelling: gramme; SI unit symbol: g) is a metric system The metric system is a that succeeded the decimalised system based on the introduced in France in the 1790s. The historical development of these systems culm ...
s: or 1 megagram (Mg). Megagram is the corresponding official SI unit with the same mass. Mg is distinct from mg, milligram. *In
pounds Pound or Pounds may refer to: Units * Pound (currency), a unit of currency * Pound sterling, the official currency of the United Kingdom * Pound (mass), a unit of mass * Pound (force), a unit of force * Rail pound, in rail profile Symbols * Po ...
: Exactly pounds (lb) by definition of the pound, or approximately . *In
short ton The short ton (symbol tn) is a mass Mass is the quantity Quantity is a property that can exist as a multitude or magnitude, which illustrate discontinuity and continuity. Quantities can be compared in terms of "more", "less", or "equal ...
s: Exactly  short tons (ST), or approximately  ST. **One short ton is exactly .National Institute of Standards and Technology. *In
long ton Long ton, also known as the imperial ton or displacement ton,Dictionary.com - ''"a unit for measuring the displacement of a vessel, equal to a long ton of 2240 pounds (1016 kg) or 35 cu. ft. (1 cu. m) of seawater."'' is the name for the unit calle ...
s: Exactly  long tons (LT), or approximately  LT. **One long ton is exactly . A tonne is the mass of one
cubic metre The cubic metre (in Commonwealth English The use of the English language English is a of the , originally spoken by the inhabitants of . It is named after the , one of the ancient that migrated from , a peninsula on the (not to b ...
of pure water: at 4 °C one thousand
litre The litre (British English British English (BrE) is the standard dialect A standard language (also standard variety, standard dialect, and standard) is a language variety that has undergone substantial codification of grammar and ...

litre
s of pure water has an absolute mass of one tonne.


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 in equivalent 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 spelt either as ''ton'' or ''tonne'' with the relevant prefix attached. *The equivalent units columns use the
short scale The long and short scales are two of several naming systems for integer powers of ten 480px, Visualisation of powers of 10 from one to 1 billion. A power of 10 is any of the integer An integer (from the Latin Latin (, or , ) is a cla ...
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 to five
significant figures Significant figures (also known as the significant digits, ''precision'' or ''resolution'') of a number in positional notation are Numerical digit, digits in the number that are reliable and absolutely necessary to indicate the quantity of som ...
. See Conversions for exact values.

ǂThough non-standard, the symbol "kt" is also used (instead of the standard symbol "kn") for
knot A knot is an intentional complication in cordage which may be practical or decorative, or both. Practical knots are classified by function, including hitches, bend Bend or bends may refer to: Materials * Bend, a curvature in a pipe, tube, o ...
, a unit of speed for aircraft and sea-going vessels, and should not be confused with kilotonne.


Alternative usage

A metric ton unit (mtu) can mean 10 kg (approximately 22 lb) within metal (e.g.
tungsten Tungsten, or wolfram, is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, ch ...

tungsten
,
manganese Manganese is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical e ...

manganese
) trading, particularly within the US. It traditionally referred to a metric ton of ore containing 1% (i.e. 10 kg) of metal. 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 of
uranium Uranium is a chemical element In chemistry, an element is a pure Chemical substance, substance consisting only of atoms that all have the same numbers of protons in their atomic nucleus, nuclei. Unlike chemical compounds, chemical elem ...

uranium
, ''MTU'' is sometimes used in the sense of ''metric ton of uranium'' (1,000 kg).NRC Collection of Abbreviations (NUREG-0544, Rev. 4), United States Nuclear Regulatory Commission
Nrc.gov (2011-03-13). Retrieved on 2011-07-10.
A gigatonne is a unit of mass often used by the coal mining industry to assess and define the extent of a coal reserve.


Use of mass as proxy for energy

The ''tonne of
trinitrotoluene Trinitrotoluene () more commonly known as TNT, or more specifically 2,4,6-trinitrotoluene, is a chemical compound A chemical compound is a chemical substance composed of many identical molecules (or molecular entity, molecular entities) com ...

trinitrotoluene
(TNT)'' is used as a proxy for energy, usually of explosions (TNT is a common
high explosive An explosive (or explosive material) is a reactive substance that contains a great amount of potential energy that can produce an explosion An explosion is a rapid expansion in volume Volume is a expressing the of enclosed by a . ...
). Prefixes are used: kiloton(ne), megaton(ne), gigaton(ne), especially for expressing
nuclear weapon yield The explosive yield of a nuclear weapon is the amount of energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which ...
, based on a specific combustion energy of TNT of about 4.2  MJ/ kg (or one thermochemical calorie per
milligram The kilogram (also kilogramme) is the SI base unit, base unit of mass in the International System of Units (SI), the metric system, having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is oft ...

milligram
). Hence, 1 t TNT = approx. 4.2  GJ, 1 kt TNT = approx. 4.2  TJ, 1 Mt TNT = approx. 4.2  PJ. The SI unit of energy is the
joule The joule ( ; symbol: J) is a derived unit of energy In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates ...

joule
. Assuming that a TNT explosion releases 1,000 small (thermochemical)
calorie The calorie is a unit of energy Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a di ...
s per gram (approx. 4.2 /g), one tonne of TNT is approx. equivalent to 4.2
gigajoules The joule ( ; symbol: J) is a SI derived unit, derived unit of energy in the International System of Units. It is equal to the energy transferred to (or work (physics), work done on) an object when a force of one Newton (unit), newton acts on tha ...

gigajoules
. In the
petroleum industry The petroleum industry, also known as the oil industry or the oil patch, includes the global processes of hydrocarbon exploration, exploration, extraction of petroleum, extraction, oil refinery, refining, Petroleum transport, transporting (often ...
the
tonne of oil equivalentThe tonne of oil equivalent (toe) is a unit of energy defined as the amount of energy released by burning one tonne of crude oil. It is approximately 42 gigajoules or 11.630 megawatt-hours, although as different crude oils have different calori ...
(toe) is a
unit of energy Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece of action (or beat) i ...
: the amount of energy released by burning one tonne of
crude oil Petroleum, also known as crude oil and oil, is a naturally occurring, yellowish-black liquid A liquid is a nearly incompressible In fluid mechanics Fluid mechanics is the branch of physics concerned with the mechanics Mech ...
, approx, 42 GJ. There are several slightly different definitions. This is ten times as much as a tonne of TNT because atmospheric oxygen is used.


Unit of force

Like the
gram The gram (alternative spelling: gramme; SI unit symbol: g) is a metric system The metric system is a that succeeded the decimalised system based on the introduced in France in the 1790s. The historical development of these systems culm ...
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 Newton most commonly refers to: * Isaac Newton (1642–1726/1727), English scientist * Newton (unit), SI unit of force named after Isaac Newton Newton may also refer to: Arts and entertainment * Newton (film), ''Newton'' (film), a 2017 Indian fil ...
.


See also

*
Metre–tonne–second system of units The metre–tonne–second or MTS system of units is a system of physical unit A unit of measurement is a definite magnitude (mathematics), magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard fo ...
*
Orders of magnitude (mass) To help compare different orders of magnitude An order of magnitude is an approximation of the logarithm of a value relative to some contextually understood reference value, usually ten, interpreted as the base of the logarithm and the represe ...
*
Ton The ton is a unit of measure A unit of measurement is a definite magnitude of a quantity Quantity is a property that can exist as a multitude or magnitude, which illustrate discontinuity and continuity. Quantities can be compared ...
**
Tonnage Tonnage Ship measurements, is a measure of the cargo-carrying capacity of a ship, and is commonly used to assess fees on commerce, commercial shipping. The term derives from the taxation paid on ''Tun (unit), tuns'' or casks of wine. In modern ...
** Ton (volume)


Notes and references


External links

*NIST Special Publication 811
''Guide for the Use of the International System of Units (SI)''
{{authority control Non-SI metric units Units of mass