The apothecaries' system of mass is an obsolete system formerly used by apothecaries (now called pharmacists or chemists) in English-speaking countries. The system was closely related to the troy system of mass, having identically sized pounds and ounces, but the two systems differed in how the ounce was subdivided.

During the 20th century, the apothecaries' system was replaced by the metric system and the SI.

Unit	Grains	Grams
Pound (12 ounces)	5760	373.241,72
Ounce (8 drams)	480	31.103,477
Dram (3 scruples)	60	3.887,934,6
Scruple (20 grains)	20	1.295,978,2
Grain	1	0.064,798,91