Science Constants - Ounce, Apothecaries' Symbol: oz (apoth) oz (ap.) Value: 3.110347680 × 10-2 kg Category: - Units of Mass Description: The Apothecaries' Ounce was used at one time as a measurement of weight for drugs and other medical substances in Britain and America. It is now obsolete, being replaced by the SI kilogram. 1 oz (ap.) = 1/12 lb (ap.) 1 oz (ap.) = 8 drachms (ap.) 1 oz (ap.) = 24 scruples (ap.) 1 oz (ap.) = 480 grains (ap.)