Troy weight

Troy weight is a system of units of mass that originated in the Kingdom of England in the 15th century[1] and is primarily used in the precious metals industry.

[2][3] The name troy is first attested in 1390, describing the weight of a platter, in an account of the travels in Europe of the Earl of Derby.

[2][4] Charles Moore Watson (1844–1916) proposes an alternative etymology: The Assize of Weights and Measures (also known as Tractatus de Ponderibus et Mensuris), one of the statutes of uncertain date from the reign of either Henry III or Edward I, thus before 1307, specifies "troni ponderacionem"—which the Public Record Commissioners translate as "troy weight".

From this, Watson suggests that 'troy' derives from the manner of weighing by balance precious goods such as bullion or drugs; in contrast to the word 'avoirdupois' used to describe bulk goods such as corn or coal, sometimes weighed in ancient times by a kind of steelyard called the auncel.

Larger amounts of precious metals are conventionally counted in hundreds or thousands of troy ounces, or in kilograms.

Troy ounces have been and are still often used in precious metal markets in countries that otherwise use International System of Units (SI).

[12][13] However, the People's Bank of China – which had been using troy measurements in minting Gold Pandas since 1982 – from 2016 specifies Chinese bullion coins in an integer numbers of grams.

[15] Since the implementation of the international yard and pound agreement of 1 July 1959, the grain measure is defined as precisely 64.79891 milligrams.

The troy ounce for trading precious metals is considered to be sufficiently approximated by 31.10 g in EU directive 80/181/EEC.

The d in dwt stands for denarius, the ancient Roman coin that equates loosely to a penny.

All Imperial systems use the same measure of mass called a grain (historically of barley), each weighing 1⁄7000 of an avoirdupois pound (and thus a little under 65 milligrams).