Tonne

The tonne is a unit of mass equal to 1,000 kilograms. It is often called a metric ton in the United States to make it clear that it is not the same as other kinds of tons. There are different kinds of tons, like the short ton and the long ton, but the tonne is based on the metric system.

One tonne is about the same as 2,204.6 pounds. This helps people understand just how heavy something is. The tonne is used around the world for measuring big amounts of things, like cargo on ships or the weight of large vehicles.

Even though it is not part of the main metric system called SI, the tonne is allowed to be used with it. Another way to say tonne is megagram, with the symbol Mg, but people use tonne more often.

Symbol and abbreviations

The symbol for the tonne is t. This symbol was chosen in 1879 and is used officially in the United States as well. It is important to use the lower-case t and not to add a period after it. Using other letters, like T or MT, can be confusing because those letters are used for other measurements, such as the tesla, a unit for magnetic fields.

When talking about energy from explosions like TNT, one megatonne of TNT equals about 4.184 petajoules.

Origin and spelling

In English, tonne is another way to say metric ton. In American and British English, tonne is usually said the same way as ton (pronounced /tʌn/), but sometimes the ending "e" is said too, like "tunnie" (/ˈtʌni/). In Australian English, people most often say it as /tɒn/. In the United States, people usually call this unit a metric ton; when someone just says ton, they usually mean a short ton of 2000 lb (907.2 kg) or, less often, a long ton of 2240 lb (1016 kg). Both ton and tonne are okay to use in Canadian English.

Both ton and tonne come from an old Germanic word used around the North Sea area since the Middle Ages. It originally meant a big cask or container called a tun. A full tun, about a metre high, could weigh about a tonne.

The spelling tonne has been used since before the SI system started in 1960. It has been used in France since 1842 and is now the normal way to write this metric weight in most English-speaking countries. In the United States, this unit was once called millier or tonneau in French, but these words are not used anymore. The old British and United States units are similar to the tonne, but they have different weights.

Conversions

A tonne is a way to measure weight, and it is equal to 1,000 kilograms. This is also the same as one million grams or one megagram, although people don't use megagrams very often.

A tonne is about 2,204.6 pounds. It is also about 1.102 short tons and 0.984 long tons. One tonne is the weight of a cubic metre of pure water at a temperature of 4 °C (which is 39 °F).

Derived units

When talking about very large amounts of the tonne, people often use words like thousands or millions of tonnes. Special names like kilotonne, megatonne, and gigatonne are used, especially when talking about the huge energy from nuclear explosions. In these cases, people might use either "ton" or "tonne" with the special prefix added.

Alternative usages

Metric ton units

A metric ton unit (mtu) can mean 10 kg (22 lb) within metal trading, especially in the United States. It traditionally referred to a metric ton of ore containing 1% (or 10 kg) of metal. In the case of uranium, MTU is sometimes used to mean metric ton of uranium (1000 kg or 2200 lb).

Use of mass as proxy for energy

The tonne of trinitrotoluene (TNT) is used as a way to measure energy, usually from explosions. Prefixes like kiloton(ne), megaton(ne), and gigaton(ne) are used, especially for showing the power of nuclear weapon yield. This is based on the energy released by TNT, which is about 4.2 MJ/kg. So, 1 t TNT is about 4.2 GJ, 1 kt TNT is about 4.2 TJ, and 1 Mt TNT is about 4.2 PJ.

The SI unit of energy is the joule. One tonne of TNT is roughly equal to 4.2 gigajoules.

In the petroleum industry, the tonne of oil equivalent (toe) is a unit of energy. It measures the energy released by burning one tonne of crude oil, which is about 42 GJ. There are a few slightly different definitions, but this is ten times more than a tonne of TNT because it uses atmospheric oxygen.

Unit of force

Like the gram and the kilogram, the tonne once gave rise to a force unit called the tonne-force, which is about 9.8 kilonewtons. This unit is also sometimes called simply "tonne" or "metric ton" but it is not accepted for use with SI.