The tonne is a unit of mass equal to 1000 kilograms. Its symbol is t. It is not an SI unit but is accepted for use with the SI, and in most of the world it is simply the working unit for anything too heavy to state comfortably in kilograms.
The name causes trouble in English. A tonne, sometimes written metric ton, is 1000 kilograms. A short ton, the American ton, is 2000 pounds or about 907 kilograms. A long ton, the British imperial ton, is 2240 pounds or about 1016 kilograms. The three differ by up to twelve per cent, which is large enough to matter in shipping and commodity contracts, so international documents normally spell out which is meant rather than relying on the word alone.
Freight and industry are its home. Ship cargo, rail wagons, steel production, cement, grain harvests and vehicle gross weights are all quoted in tonnes. Bridge and crane load ratings use it, and so does the deadweight tonnage of a ship, although that particular term measures carrying capacity rather than the mass of the vessel itself.
Climate accounting has given the tonne a second public life. National and corporate emissions are reported in tonnes of carbon dioxide equivalent, and carbon markets price allowances per tonne. A single average petrol car emits roughly two tonnes of carbon dioxide a year, which is why the unit appears in policy documents far outside engineering.
Energy accounting borrows the word for a quantity that is not a mass at all. The tonne of oil equivalent is defined as the energy released by burning one tonne of crude oil, about 41.87 gigajoules, and national energy balances are published in millions of them. A tonne of coal equivalent serves the same purpose at a different value. These are conventions rather than measurements: no particular tonne of oil delivers exactly that figure, but fixing one lets gas, coal, nuclear output and renewables be added together on a single scale. Readers of energy statistics therefore meet the tonne twice, once as a mass of fuel and once as a package of energy.
One tonne equals 1000 kilograms, about 2204.62 pounds, or approximately 1.10231 short tons.
| Unit | Symbol | 1 Tonne equals | 1 of these equals | Converter |
|---|---|---|---|---|
| Nanogram | ng | 1 × 1015 ng | 1 × 10-15 t | Tonnes to Nanograms |
| Microgram | μg | 1000000000000 μg | 1 × 10-12 t | Tonnes to Micrograms |
| Milligram | mg | 1000000000 mg | 0.000000001 t | Tonnes to Milligrams |
| Gram | g | 1000000 g | 0.000001 t | Tonnes to Grams |
| Kilogram | kg | 1000 kg | 0.001 t | Tonnes to Kilograms |
| Grain | gr | 15432358.3529 gr | 0.00000006479891 t | Tonnes to Grains |
| Dram | dr | 564383.391193 dr | 0.00000177184519531 t | Tonnes to Drams |
| Ounce | oz | 35273.9619496 oz | 0.000028349523125 t | Tonnes to Ounces |
| Pound | lb | 2204.62262185 lb | 0.00045359237 t | Tonnes to Pounds |
| Stone | st | 157.473044418 st | 0.00635029318 t | Tonnes to Stones |
| Hundredweight | cwt | 19.6841305522 cwt | 0.05080234544 t | Tonnes to Hundredweights |
| Long ton | t | 0.984206527611 t | 1.0160469088 t | Tonnes to Long tons |