apothecaries' measure

In contrast with apothecaries' weight, apothecaries' measure is a system both recent and short-lived. It seems to have arisen with the United Kingdom's defining of the new imperial gallon in 1824, and is fully described at least as early as 1878 in the Weights and Measures Act. In the United Kingdom, the 1963 Weights and Measures Act provided for the abolition of the minim, scruple, and fluid drachm, all already obsolete.  Actual delegalization occurred on 1 February 1971.

British Apothecaries’ Measure, 1878 to 1 February 1971ยน

imperial gallon

fluid ounce

160

fluid drachm

8

1,280

fluid scruple

3

24

3,840

minim

20

60

480

76,800

0.059 mL

1.184 mL

3.55163 mL

28.41 mL

4.546 L

0.96
U.S. minim

19.2
 U.S. minims

0.96
fluid dram (US)

0.96
U.S fluid ounce

1.20095
U.S. gallons

1. Schedule 2, Weights and Measures Act 1878 (41 & 42 Victoria c.48)

Pharmacists in the United States adopted a similar system, but instead of subdividing the imperial fluid ounce, they subdivided the U.S. fluid ounce. In the United States, apothecaries' measure was gradually overtaken by milliliters, though even today if a prescription for a liquid is actually compounded by the pharmacist, it may be supplied in a bottle embossed with a scale marked with the symbol for fluid drams.

U.S. Apothecaries’ Measure, to Present

U.S. gallon

U.S. liquid pint

8

U.S. fluid ounce

16

128

fluid dram

8

128

1,024

minim

60

480

7,680

61,440

0.062 mL

3.697 mL

29.57 mL

473 mL

3.785 L

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