Long ton, also known as the imperial ton or weight ton, is the name for the unit called the "ton" in the avoirdupois or Imperial system of measurements standardised in the thirteenth century that is used in the United Kingdom and several other Commonwealth countries alongside the French metrication invented in 1799. 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 in trade of elemental sulfur, and was the unit prescribed for warships by the Washington Naval Treaty 1922—for example battleships were limited to a displacement of 35,000 long tons (36,000 t; 39,000 short tons).