High Quality Content by WIKIPEDIA articles! The stone is a unit of measure, which in practice is usually a mass of about 6.35 kilograms. When it ceased to be legal for trade in United Kingdom in 1985, it was defined in British legislation as being a weight or mass equal to 14 pounds. It was also formerly used in several Commonwealth countries. Eight stones make a hundredweight in the Imperial system. Given its imprecise definition, it is arguable whether one should use kilograms or newtons as the equivalent SI unit.