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The tonne ( or ; symbol: t) is a unit of mass equal to 1000 
kilogram The kilogram (also kilogramme) is the unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially. ...
s. It is a non-SI unit accepted for use with SI. It is also referred to as a metric ton to distinguish it from the non-metric units of the
short ton The short ton (symbol tn) is a measurement unit equal to . It is commonly used in the United States, where it is known simply as a ton, although the term is ambiguous, the single word being variously used for short, long, and metric ton. The var ...
(
United States customary units United States customary units form a system of measurement units commonly used in the United States and U.S. territories since being standardized and adopted in 1832. The United States customary system (USCS or USC) developed from English uni ...
), and the long ton ( British imperial units). It is equivalent to approximately 2204.6 pounds, 1.102 short tons, and 0.984 long tons. 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, through which its 59 member-states act together on measurement standards in four areas: chemistr ...
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 an agency of the United States Department of Commerce whose mission is to promote American innovation and industrial competitiveness. NIST's activities are organized into physical s ...
(NIST). It is a symbol, not an abbreviation, and should not be followed by a period. Use of
minuscule Letter case is the distinction between the letters that are in larger uppercase or capitals (or more formally ''majuscule'') and smaller lowercase (or more formally ''minuscule'') in the written representation of certain languages. The writing ...
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 defined by that convention to be , which is the approximate energy released in the detonation of a ...
units of energy, one megatonne of TNT is equivalent to approximately 4.184
petajoule The joule ( , ; symbol: J) is the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force applied ...
s.


Origin and spelling

In English, ''tonne'' is an established spelling alternative to ''metric ton''. In the United States and United Kingdom, 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 measurement unit equal to . It is commonly used in the United States, where it is known simply as a ton, although the term is ambiguous, the single word being variously used for short, long, and metric ton. The var ...
of and to a lesser extent to a long ton of , the ''tonne'' is rarely used in speech or writing. Both terms are acceptable in Canadian usage. ''Ton'' and ''tonne'' are both derived from a Germanic word in general use in the
North Sea The North Sea lies between Great Britain, Norway, Denmark, Germany, the Netherlands and Belgium. An epeiric sea on the European continental shelf, it connects to the Atlantic Ocean through the English Channel in the south and the Norwegian ...
area since the
Middle Ages In the history of Europe, the Middle Ages or medieval period lasted approximately from the late 5th to the late 15th centuries, similar to the post-classical period of global history. It began with the fall of the Western Roman Empire ...
(cf.
Old English Old English (, ), or Anglo-Saxon, is the earliest recorded form of the English language, spoken in England and southern and eastern Scotland in the early Middle Ages. It was brought to Great Britain by Anglo-Saxon settlers in the mid-5th ...
and
Old Frisian Old Frisian was a West Germanic language spoken between the 8th and 16th centuries along the North Sea coast, roughly between the mouths of the Rhine and Weser rivers. The Frisian settlers on the coast of South Jutland (today's Northern Fries ...
''tunne'',
Old High German Old High German (OHG; german: Althochdeutsch (Ahd.)) is the earliest stage of the German language, conventionally covering the period from around 750 to 1050. There is no standardised or supra-regional form of German at this period, and Old Hig ...
and
Medieval Latin Medieval Latin was the form of Literary Latin used in Roman Catholic Western Europe during the Middle Ages. In this region it served as the primary written language, though local languages were also written to varying degrees. Latin functioned ...
,
German German(s) may refer to: * Germany (of or related to) **Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...
and
French French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Franc ...
''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 people English may also refer to: Peoples, culture, and language * ''English'', an adjective for something of, from, or related to England ** English national ...
-speaking countries. In the United States, the unit was originally referred to using the
French French (french: français(e), link=no) may refer to: * Something of, from, or related to France ** French language, which originated in France, and its various dialects and accents ** French people, a nation and ethnic group identified with Franc ...
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 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 unit of mass in the International System of Units (SI), having the unit symbol kg. It is a widely used measure in science, engineering and commerce worldwide, and is often simply called a kilo colloquially. ...
s: by definition. *In
gram The gram (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram. Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to th ...
s: or 1 megagram (Mg). Megagram is the corresponding official SI unit with the same mass. Mg is distinct from mg, milligram. *In pounds: Exactly pounds (lb) by definition of the pound, or approximately . *In
short ton The short ton (symbol tn) is a measurement unit equal to . It is commonly used in the United States, where it is known simply as a ton, although the term is ambiguous, the single word being variously used for short, long, and metric ton. The var ...
s: Exactly  short tons (ST), or approximately  ST. **One short ton is exactly .National Institute of Standards and Technology. *In long tons: 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 and international spelling as used by the International Bureau of Weights and Measures) or cubic meter (in American English) is the unit of volume in the International System of Units (SI). Its symbol is m ...
of pure water: at 4 °C one thousand
litre The litre (international spelling) or liter (American English spelling) (SI symbols L and l, other symbol used: ℓ) is a metric unit of volume. It is equal to 1 cubic decimetre (dm3), 1000 cubic centimetres (cm3) or 0.001 cubic metre (m3 ...
s of pure water has an absolute mass of one tonne.


Derived units

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 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 spelled 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 which use some of the same terms for different magnitudes. For whole numbers smaller than 1,000,000,000 (109), such as one thousand or one million, the ...
large-number naming system currently used in most English-language countries, e.g. 1 billion = 1000 million = .

Values in the equivalent short and long tons columns are rounded to five
significant figures Significant figures (also known as the significant digits, ''precision'' or ''resolution'') of a number in positional notation are digits in the number that are reliable and necessary to indicate the quantity of something. If a number expres ...
. 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, bends, loop knots, and splices: a ''hitch'' fastens a rope to another object; a ...
, a unit of speed for aircraft and sea-going vessels, and should not be confused with kilotonne.


Alternative usages


Metric ton units

A metric ton unit (mtu) can mean 10 kg (approximately 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. The following excerpt from a mining geology textbook describes its usage in the particular case of tungsten: In the case of
uranium Uranium is a chemical element with the symbol U and atomic number 92. It is a silvery-grey metal in the actinide series of the periodic table. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons. Uranium is weak ...
, ''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.


Use of mass as proxy for energy

The ''tonne of
trinitrotoluene Trinitrotoluene (), more commonly known as TNT, more specifically 2,4,6-trinitrotoluene, and by its preferred IUPAC name 2-methyl-1,3,5-trinitrobenzene, is a chemical compound with the formula C6H2(NO2)3CH3. TNT is occasionally used as a reage ...
(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 if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An ...
). 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 released when that particular nuclear weapon is detonated, usually expressed as a TNT equivalent (the standardized equivalent mass of trinitrotoluene which, if detonated, would prod ...
, based on a specific combustion energy of TNT of about 4.2  MJ/ kg (or one thermochemical calorie per 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 the unit of energy in the International System of Units (SI). It is equal to the amount of work done when a force of 1 newton displaces a mass through a distance of 1 metre in the direction of the force appli ...
. One tonne of TNT is approximately equivalent to 4.2 gigajoules. In the
petroleum industry The petroleum industry, also known as the oil industry or the oil patch, includes the global processes of exploration, extraction, refining, transportation (often by oil tankers and pipelines), and marketing of petroleum products. The larg ...
the
tonne of oil equivalent The 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 calorifi ...
(toe) is a unit of energy: the amount of energy released by burning one tonne of
crude oil Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crude ...
, 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 (originally gramme; SI unit symbol g) is a unit of mass in the International System of Units (SI) equal to one one thousandth of a kilogram. Originally defined as of 1795 as "the absolute weight of a volume of pure water equal to th ...
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 The newton (symbol: N) is the unit of force in the International System of Units (SI). It is defined as 1 kg⋅m/s, the force which gives a mass of 1 kilogram an acceleration of 1 metre per second per second. It is named after Isaac Newton in ...
. 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.


See also

*
Metre–tonne–second system of units The metre–tonne–second or MTS system of units is a system of physical units. It was invented in France, hence the unit names ''sthène'' and ''pièze'', and became its legal system between 1919 and 1961 ("décret" 5 May 1961, "Journal Officie ...
*
Orders of magnitude (mass) To help compare different orders of magnitude, the following lists describe various mass levels between 10−59  kg and 1052 kg. The least massive thing listed here is a graviton, and the most massive thing is the observable universe. ...
*
Ton Ton is the name of any one of several units of measure. It has a long history and has acquired several meanings and uses. Mainly it describes units of weight. Confusion can arise because ''ton'' can mean * the long ton, which is 2,240 pounds ...
**
Tonnage Tonnage is a measure of the cargo-carrying capacity of a ship, and is commonly used to assess fees on commercial shipping. The term derives from the taxation paid on ''tuns'' or casks of wine. In modern maritime usage, "tonnage" specifically r ...
**
Ton (volume) Ton is the name of any one of several units of measure. It has a long history and has acquired several meanings and uses. Mainly it describes units of weight. Confusion can arise because ''ton'' can mean * the long ton, which is 2,240 pounds ...


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