A grain is a unit of measurement of mass that is nominally based upon the mass of a single seed of a cereal. The grain is the only unit of mass measure common to the three traditional English mass and weight systems; the obsolete Tower grain was, by definition, exactly /64 of a troy grain. Since 1958, the grain or troy grain measure has been defined in terms of units of mass in the International System of Units as precisely 64.79891 milligrams. Thus, \(1 gram \approx 15.4323584 grains\). There are precisely 7,000 grains per avoirdupois pound in the imperial and U.S. customary units, and 5,760 grains in the Troy pound.