Long ton, also known as the imperial ton or displacement ton, is the name for the unit called the "ton" in the avoirdupois system of weights or Imperial system of measurements. It was standardised in the thirteenth century. It is used in the United Kingdom and several other Commonwealth of Nations countries alongside the mass-based metric tonne defined in 1799, as well as in the United States for bulk commodities.
It is not to be confused with the short ton, a unit of weight equal to 2,000 pounds (907.18474 kg) used in the United States, and in Canada before metrication, also referred to simply as a "ton".
A long ton is defined as exactly 2,240 pounds. The long ton arises from the traditional British measurement system: A long ton is 20 hundredweight (cwt), each of which is 8 stone (1 stone = 14 pounds). Thus a long ton is 20 × 8 × 14 lb = 2,240 lb.
A long ton, also called the weight ton (W/T), imperial ton, or displacement ton, is equal to:
- 2,240 pounds or 1,016 kilograms or 1.016 metric tons
- 12% more than the 2,000 pounds of the North American short ton
- the weight of 35 cubic feet (0.99 m3) of salt water with a density of 64 pounds per cubic foot (1.03 g/cm3)
The long ton remains in use in both the United Kingdom and the United States, where it is commonly used in measuring the displacement of ships, the volume-to-carrying-weight of fuels, and in trade of baled commodities and bulk goods like iron ore and elemental sulfur. The long ton was the unit prescribed for warships by the Washington Naval Treaty of 1922—for example battleships were limited to a displacement of 35,000 long tons (36,000 t; 39,000 short tons).
To comply with the practices of the European Union, the British Imperial ton was explicitly excluded from use for trade by the United Kingdom's Weights and Measures Act of 1985.
The long ton remains in informal use by some heritage rail companies and remains on a limited number of weight limit signs on roads (usually in remote areas away from major towns and cities where tonnes are used).
- Short ton, equal to 2,000 lb (907.2 kg).
- Tonnage, volume measurement used in maritime shipping, originally based on 100 cubic feet (2.83 m3).
- Tonne, also known as a metric ton (t), equal to 1,000 kg (2,205 lb) or 1 megagram.