Troy weight

Troy weight

Troy weight is a system of units of mass customarily used for precious metals, black powder, and gemstones.

Named after Troyes, France, the troy system of weights was known to exist in medieval times. One cubic inch of distilled water, at 62 °F (17 °C), and at a barometric pressure of 30 inches of mercury, was determined to weigh 252.458 troy grains (gr). [cite book | last=Wightman | first=S. | coauthors=Blanchard, William | title=Wightman's Arithmetical Tables | location=Westminster | publisher=S. Wightman | year=1840 | oclc=43196919]

Troy ounce

The troy ounce (ozt) is 480 grains, somewhat heavier than an avoirdupois ounce (437.5 grains).cite web | title=Troy Ounce | url= | work=WordNet 3.0, | publisher=Princeton University | accessdate=2008-01-10] A grain is exactly 64.79891 mg; hence one troy ounce is exactly 31.1034768 g, about 10 percent more than the avoirdupois ounce, which is exactly 28.349523125 g. The troy ounce is the only ounce used in the pricing of precious metals, gold, platinum, and silver. The grain, which is identical in both the troy and avoirdupois systems, is used to measure arrow and arrowhead weights in archery and bullets and powder weights in ballistics. Grains were long used in medicine but have been largely replaced by milligrams.

Troy pound

The troy pound (troy) is 5,760 gr (≈ 373.24 g, 12 ozt), while an avoirdupois pound is 7,000 gr (≈ 453.59 g).

There are 12 troy ounces per troy pound, rather than 16 avoirdupois ounces (oz) in the avoirdupois pound (lb) as in the more common avoirdupois system. The avoirdupois pound is 14712 (≈ 14.583) troy ounces, since troy ounces are larger than avoirdupois ounces.

In Scotland the Incorporation of Goldsmiths of the City of Edinburgh used a system in multiples of sixteen. ("See Assay-Master's Accounts, 1681-1702, on loan from the Incorporation to the National Archives of Scotland.") Thus there were 16 drops to the troy ounce, 16 ounces to the troy pound, and 16 pounds to the troy stone. The Scots had several other ways of measuring precious metals and gems, but this was the common usage for silver and gold.


The troy system was used in the Apothecaries' system, but with different further subdivisions.

Relationship to British coinage

The troy system was the basis for the pre-decimalisation British system of coinage introduced by Henry II of England, in which the penny was literally one pennyweight of silver. One pound sterling was equal to twenty shillings, with each shilling equal to twelve pennies. Thus, one pound sterling equals 240 pennyweights, or one troy pound of sterling silver.

ee also

* Carat (mass)
* Conversion of units
* Mark (weight) - essay on the history of the Troy Ounce with many links to further reading.


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  • Troy weight — Troy Troy, n. Troy weight. [1913 Webster] {Troy weight}, the weight which gold and silver, jewels, and the like, are weighed. It was so named from Troyes, in France, where it was first adopted in Europe. The troy ounce is supposed to have been… …   The Collaborative International Dictionary of English

  • troy-weight — ● troy ou troy weight nom masculin Système de poids anglais, employé pour les métaux précieux et les pierreries, dans lequel la pound troy (373 g) vaut 12 ounces, et l ounce 480 grains …   Encyclopédie Universelle

  • troy weight — n a series of units of weight based on a pound of 12 ounces and an ounce of 480 grains or 31.103 grams …   Medical dictionary

  • troy weight — [ trɔı ,weıt ] noun uncount a system for measuring the weight of jewels and metals such as gold and silver …   Usage of the words and phrases in modern English

  • troy weight — [ˈtrɔı weıt] n [U] [Date: 1400 1500; Origin: Troyes city in northern France] a system of measuring weights in Britain and the US, used especially for weighing gold, silver etc …   Dictionary of contemporary English

  • troy weight — troy′ weight n. wam a system of weights in use for precious metals and gems, in which a pound equals 12 ounces (0.373 kg) and an ounce equals 20 pennyweights or 480 grains (31.103 grams) …   From formal English to slang

  • troy weight — n. [ME, after TROYES2, where first used at medieval fairs] a system of weights for gold, silver, precious stones, etc.: see the table of weights and measures in the Reference Supplement …   English World dictionary

  • troy weight — noun a system of weights used for precious metals and gemstones; based on a 12 ounce pound and an ounce of 480 grains • Syn: ↑troy • Hypernyms: ↑system of weights, ↑weight • Part Meronyms: ↑troy unit * * * noun …   Useful english dictionary

  • troy weight — /trɔɪ weɪt/ noun a system of measurement of weight used for gold and other metals, such as silver and platinum COMMENT: Troy weight is divided into grains, pennyweights (24 grains = 1 pennyweight), ounces (20 pennyweights = 1 ounce) and pounds… …   Dictionary of banking and finance

  • troy weight — a system of weights in use for precious metals and gems (formerly also for bread, grain, etc.): 24 grains = 1 pennyweight (1.555 grams); 20 pennyweights = 1 ounce (31.103 grams); 12 ounces = 1 pound (0.373 kilogram). The grain, ounce, and pound… …   Universalium

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