troy weight

The name comes from Troyes, a city in France. During the Middle Ages it was the site of a major annual trade fair that drew merchants from most of Europe.

1

In the English-speaking world, at least as early as the 10^th century – present, a system of units of mass used for precious metals and other valuables, and for bread. Its subdivision is heavily influenced by the Romans' subdivision of the libra. The smallest unit, the grain, is traditionally the mass of a grain of barley.

Grain for grain, ounce for ounce, and pound for pound, troy weight is the same as apothecaries' weight, but it is subdivided differently. The troy grain is the same as the avoirdupois grain.

					mast*
				troy pound	2½
			troy ounce	12	30
		pennyweight	20	240	600
	grain	24	480	5760	14,400
before changes in 1588 and 1758	64.76 mg	1554.2 mg	31.08	373.01 g	932.52 g
after 1758	64.798 91 mg	1555.173 84 mg	31.103 476 8 g	373.241 721 6 g	933.104304 g
avoirdupois	1 gr	0.054 857 14 oz	1.097 143 oz	13.165 71 oz	2.057 142 lb

*The mast was obsolete by the 17th century.

Simpson and Connor¹ have made a convincing case that in the early medieval period, the troy ounce was identical with the silver ounce of Bruges.

In the United Kingdom, the troy pound was abolished in 1878² and the troy ounce restricted to precious metals. In 1976³ the pennyweight was made no longer legal for trade. In 1985⁴, the troy ounce was redefined as 12/175 of a pound, and the grain was made no longer legal for trade.

In the United States, troy weight remains legal, and in fact in 1982 guidance for its use was added to the Uniform Regulation for the Method of Sale of Commodities, model legislation proposed for adoption by individual states by the National Conference on Weights and Measures. (See page 20 of the regulation.)

1. A. D. C. Simpson and R. D. Connor.
The Mass of the English Troy Pound in the Eighteenth Century.
Annals of Science, vol. 61, pages 321-349 (2004)

2. Weights and Measures Act, 1878. 41 & 42 Victoria, c 49.

3. Weights and Measures Act, 1976, Elizabeth II, c 77.

4. Weights and Measures Act, 1985.

2

In Holland, ? – 19th century, a system of weights used for gold and silver. As a very well-standardized weight by the standards of the time, the Dutch as became the basis of other national weight systems, for example, Swedish weights before 1830.

						pond trooisch
						mark trooisch		2
						once	8	16
					lood	2	16	32
	engels or esterling				10	20	160	320
			vierling	4	40	80	640	1280
		troyken	2	8	80	160	1280	2560
	deusken	2	4	16	160	320	2560	5120
as	2	4	8	32	320	640	5120	10240
48.06252 mg	96.125 mg	192.25 mg	384.50 mg	1.538 g	15.38 g	30.76 g	246.08 g	492.16772 g