tower "wheat" grain was defined as exactly 45/64 (? 3/4) of the troy "barley" grain.

Since the implementation of the international yard and pound agreement of 1 July 1959, the grain or troy grain (symbol: gr) measure has been defined in terms of units of mass in the International System of Units as precisely . One gram is thus approximately equivalent to . The unit formerly used by jewellers to measure pearls, diamonds, and other