A stone is a unit of mass within the Imperial units system used in the United Kingdom and Ireland, and formerly in a number of Commonwealth countries. It is equal to 14 pounds avoirdupois, i.e. 6.35029 kilograms.
Though formerly used for some agricultural commodities, including at the retail or household level (potatoes, for example, were traditionally sold in 7 pound or 14 pound quantities), the stone is now used almost exclusively for expressing human body weight; a person would normally describe themselves as weighing, say, "11 stone 4", meaning 11 stone and four pounds. In that context, it is virtually universal in everyday use, though for medical or other technical purposes kilograms are used.
The use of stones as a unit of weight for any purpose is unknown in the United States and Canada, as is the use of pounds on their own for body weight in Britain or Ireland.
See also