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A stone is a unit of mass in the Imperial system of weights and measures formerly used in the United Kingdom, Ireland, and most Commonwealth countries. It is equal to 14 pounds avoirdupois, or 6.35029318 kilograms.
It was frequently used in the past for weighing agricultural commodities. Potatoes, for example, were traditionally sold in stones or half-stones (14-pound or 7-pound quantities). Though no longer an official unit of measure – in medical and other technical contexts kilograms are used – the stone remains almost universally popular for use in Britain and Ireland as a means of expressing human body weight. A person in these countries would normally describe themselves as weighing, for example, "11 stone 4" (11 stone and 4 pounds).
In the United States and Canada, where stone as a unit of weight is generally unknown, a person would normally describe themselves as weighing "158 pounds" (using the same amount of weight as in the previous example). This usage of pounds alone to express body weight is very unusual in Britain and Ireland.