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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. It is important to distinguish, however, between the origin of the name, and the origin of the magnitudes making up the system.

1

Convert between troy ounces or troy pounds and other major units of mass.

Download an Excel spreadsheet for calculating in this weight system.

In the English-speaking world, at least as early as the 10ᵗʰ 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.

*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.

sources

1

That all the Goldsmiths of England shall gild no Silver worse than of the Allay of the English Sterling, and that they take for a Pound of Troy gilt but Forty-Six Shillings Eight-pence at the most, and of greater Weight, and less, according to the Quantity and Rate of the same sum.

2 Henry V Statute 2, chapter 4. (1414).
The first mention of troy weight in English law. The original is in Norman French; this is an old translation.

2

Item, Forasmuch as great Scarcity of White Money is within the Realm, because that Silver is bought and sold not coined, at the price of xxxij s. the Pound of Troy, whereas the same Pound is no more of Value at the Coin than xxxij. s. abated for the Coinage Twelve-pence;…

2 Henry VI chapter 16 (1423).
As F. G. Skinner (1967) points out, “It is quite evident from these two statutes, that among English goldsmiths and silversmiths the Troy System was already well-established.”

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.

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Last revised: 17 April 2012.