Conversion from 100 Hundredweights to Tonnes

Information about the Hundredweight (cwt)

The hundredweight is a unit of mass whose value depends on which side of the Atlantic you are standing. The imperial or long hundredweight is 112 pounds, about 50.802 kilograms. The US or short hundredweight is 100 pounds, about 45.359 kilograms. Its symbol is cwt, from the Latin centum and the English weight.

The name promises a hundred and the imperial version delivers a hundred and twelve, which looks like an error until the arithmetic behind it is seen. Twenty hundredweight make a long ton of 2240 pounds, and a hundredweight is eight stone of fourteen pounds each. The chain of halvings and doublings that runs from the pound to the ton only closes neatly if the intermediate unit is 112, so the number is a consequence of the system rather than a mistake in it.

Its working life was in bulk trade. Coal, cement, grain, potatoes and fertiliser moved by the hundredweight, and sack sizes were built around it: the standard British coal sack held one hundredweight, which is why a coal merchant's cart was rated in a number of hundredweight rather than in tons. Vans and light trucks were once classified the same way, and the phrase survives in some vehicle names.

In the United States the short hundredweight is still used in agricultural markets, where livestock, grain and milk prices are quoted per hundredweight rather than per pound or per ton. Elsewhere the unit has largely given way to the tonne and the kilogram, and its main modern role is to make old records intelligible.

Continental Europe kept a cousin of it under a different name. The quintal, from the Arabic qintar by way of medieval Latin, served the same purpose in French, Spanish, Italian and Portuguese trade, and when the metric system arrived it was simply redefined as a round 100 kilograms. That metric quintal is still the unit in which grain harvests are reported across much of southern Europe, Latin America and India, and it sits close enough to the imperial hundredweight of 50.8 kilograms that old and new figures can look deceptively similar. The parallel is instructive: both units survived because a sack a strong worker could handle is a more natural quantity than any round metric mass.

One imperial hundredweight equals 112 pounds, about 50.802 kilograms, or 8 stone.

Information about the Tonne (t)

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.