Long ton (weight ton or Imperial ton) is the name for the unit called the "ton" in the avoirdupois or Imperial system of measurements that was used in the United Kingdom and several other Commonwealth countries before metrication. One long ton is equal to 2,240 pounds (1,016 kg), 12% larger than a short ton and 1.6% larger than the 1,000-kilogram (2,205 lb) tonne, or 35 cubic feet (0.9911 m3) of salt water with a density of 64 lb/cu ft (1.025 g/ml). It has some limited use in the United States, most commonly in measuring the displacement of ships, and was the unit prescribed for warships by the Washington Naval Treaty 1922—for example battleships were limited to a mass of 35,000 long tons (36,000 t; 39,000 short tons).
- A long ton is defined as exactly 2,240 pounds (a little over 1.016 tonnes, see below).
- A pound is defined as exactly 453.59237 grams.
- A long ton then is exactly 1,016,046.9088 grams, which is approximately 1,016 kg – conveniently close to a (metric) tonne.
The long ton arises from the traditional British measurement system: A long ton is 20 hundredweight, each of which is 8 stone, which is defined as 14 pounds. Thus a long ton is 20 × 8 × 14 lb = 2,240 lb.
- 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.