Convert from grain to ton [metric]

Unit Definition (grain)
The grain is a traditional unit of weight. The grain, equal to 1/480 troy ounce, or exactly 64.798 91 milligrams, was the legal foundation of traditional English weight systems, with various pounds being defined as a specified number of grains: 5760 grains in a troy pound and 7000 grains in an avoirdupois pound, for example. In the version of the troy system used by jewelers, there are 24 grains in a pennyweight and 20 pennyweight in an ounce. In the version used by apothecaries, there are 20 grains in a scruple, 3 scruples in a dram, and 8 drams in an ounce. Originally the grain was defined in England as the weight of a barleycorn. This made the English grain larger the corresponding grain units of France and other nations of the Continent, because those units were based on the weight of the smaller wheat grain.

Unit Definition (ton [metric])
The ton is a traditional unit of weight equal to 20 hundredweight. In the United States and Canada, there are 100 pounds in the hundredweight and exactly 2000 pounds (907.185 kilograms) in the ton. In Britain, there are 112 pounds in the hundredweight and 2240 pounds (1016.047 kilograms) in the ton. To distinguish between the two units, the British ton is called the long ton and the American one is the short ton. In old England, a "tun" was a large cask used to store wine. Because these tuns were of standard size, more or less, the tun came to represent both a volume unit, indicating the capacity of a cask, and also a weight unit, indicating the weight of a cask when it was full.