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. Sometimes "ap" is added to the front of the unit to identify it as part of the apothecaries' system. Similar systems had been in use in other European countries.
During the first half of the 20th century, the apothecaries' system was replaced by the metric system.
| Unit | Symbol | Division | Grains | SI units |
|---|---|---|---|---|
| Pound | ℔ | 12 ounces | 5760 | 373.242 g |
| Ounce | ℥ | 8 drams | 480 | 31.103 g |
| Drachm | ʒ | 3 scruples | 60 | 3.888 g |
| Scruple | ℈ | 20 grains | 20 | 1.296 g |
| Grain | G | [ 64.79891 mg ] | 1 | 64,8 mg |
After the introduction of the imperial gallon (1824), some English apothecaries started using a system of volume that was closely related to the system of mass, taking advantage of the approximate equivalence of weight and volume of water and similar fluids with equal-named units. It was abolished effective 1 January 1971 and had fallen out of use already.
| Unit | Symbol | Division | Minims | SI units |
|---|---|---|---|---|
| Gallon | gal. | 8 pints | 76800 | 4.54609 L |
| Pint | pt. | 20 ounces | 9600 | 568.26 mL |
| Ounce | oz. | 8 drachms | 480 | 28.413 mL |
| Drachm | dr. | 3 scruples | 60 | 3.5516 mL |
| Scruple | sc. | 20 minims | 20 | 1.1839 mL |
| Minim | min. | 1 | 0.0592 mL |