Grain
Unit of mass
A grain is a unit of measurement of mass, and in the troy weight, avoirdupois, and apothecaries' systems, equal to exactly 64.79891 milligrams. It is nominally based upon the mass of a single ideal seed of a cereal. Wikipedia
1 gr in: is equal to
Avoirdupois: 1⁄7000 pound
SI units: 64.79891 mg
Symbol: gr
Troy: 1⁄5760 troy pound
Unit of: Mass
Unit system: Troy weight, avoirdupois weight, apothecaries' weight