Apothecaries' System - English-speaking Countries

English-speaking Countries

Weights: UK (Imperial) and US

Weight (abbreviation)	pound (℔)	ounce (℥)	dra(ch)m (ʒ)	scruple (℈)	grain (gr.)
	1 ℔	12 ℥	96 ʒ	288 ℈	5,760 gr.
		1 ℥	8 ʒ	24 ℈	480 gr.
			1 ʒ	3 ℈	60 gr.
				1 ℈	20 gr.
metric equivalent	373 g	31.1 g	3.89 g	1.296 g	64.8 mg

See also: Imperial units See also: United States customary units

The traditional English apothecaries' system of weights is as shown in the table, the pound, ounce and grain being identical to the troy pound, ounce and grain. In the United Kingdom, a reform in 1824 made the troy pound the primary weight unit (a role in which it was superseded half a century later by the Avoirdupois pound), but this had no effect on apothecaries' weights. However, the Medicinals Act of 1858 completely abolished the apothecaries' system in favour of the standard Avoirdupois system. In the United States, the apothecaries' system remained official until it was abolished in 1971 in favour of the metric system.

From the pound down to the scruple, the English apothecaries' system was a subset of the Roman weight system except that the troy pound and its subdivisions were slightly heavier than the Roman pound and its subdivisions. Similar systems were used all over Europe, but with considerable local variation described below under Variants.

The English-speaking countries also used a system of units of fluid measure, or in modern terminology volume units, based on the apothecaries' system. A volume of liquid that was approximately that of an apothecaries' ounce of water was called a fluid ounce, and was divided into fluid drachms and sometimes also fluid scruples. The analogue of the grain was called a minim. The Imperial and US systems differ in the size of the basic unit (the gallon or the pint, one gallon being equal to eight pints), and in the number of fluid ounces per pint. Apothecaries' systems for volumes were internationally much less common than those for weights. Before introduction of the Imperial Units in the UK, all apothecaries' measures were based on the wine gallon, which survived in the US under the name liquid gallon or wet gallon.

The wine gallon was abolished in Britain in 1824, and this system was replaced by a new one based on the newly introduced Imperial gallon. Since the Imperial gallon is 20% more than the liquid gallon, the same is true for the Imperial pint in relation to the liquid pint. This explains why the number of fluid ounces per gallon had to be adjusted in the new system so that the fluid ounce was not changed too much by the reform. Even so, the modern UK fluid ounce is 4% less than the US fluid ounce, and the same is true for the smaller units. For some years both systems were used concurrently in the UK.

Measures: US (and UK before 1824) liquid pt fl. ounce fl. dram fl. scruple minim 1 liq pt 16 f℥ 128 fʒ 384 f℈ 7,680 ♏ 1 f℥ 8 fʒ 24 f℈ 480 ♏ 1 fʒ 3 f℈ 60 ♏ 1 f℈ 20 ♏ 473 ml 29.6 ml 3.70 ml 1.23 ml 0.062 ml Key: pt = pint, fl. = fluid

Measures: UK (Imperial) pint fl. ounce fl. drachm fl. scruple minim 1 pt 20 f℥ 160 fʒ 480 f℈ 9,600 ♏ 1 f℥ 8 fʒ 24 f℈ 480 ♏ 1 fʒ 3 f℈ 60 ♏ 1 f℈ 20 ♏ 568 ml 28.4 ml 3.55 ml 1.18 ml 0.059 ml Key: fl. = fluid

Apothecaries' measures eventually fell out of use in the UK and were officially abolished in 1971. In the US, they are still occasionally used, for example with prescribed medicine being sold in four ounce (℥ iv) bottles.