traditional system of weight in the British Isles used for the measuring and dispensing of pharmaceutical items and based on the grain, scruple (20 grains), dram (3 scruples), ounce (8 drams), and pound (12 ounces). The apothecaries' grain is equal to the troy (troy weight) and avoirdupois (avoirdupois weight) grains and represents ¹/_5,760 part of the troy and apothecaries' pound and ¹/_7,000 part of the avoirdupois pound. One apothecaries' pound equals approximately 0.82 avoirdupois pound, 373.24 grams, and 0.37 kilogram.

Apothecaries' weight was used officially in both the United States and Great Britain until 1858. In that year, under the authority of the Medical Act, Great Britain adopted the avoirdupois system for dispensing medicines. Apothecaries' weight is still common in the United States. In recent years, however, the metric system has gradually replaced it for dispensing medicines.