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Troy weight is a system of Physical unit of mass that originated in the Kingdom of England in the 15th century and is primarily used in the industry. The troy weight units are the grain, the pennyweight (24 grains), the troy ounce (20 pennyweights), and the troy pound (12 troy ounces). The troy grain is equal to the grain unit of the avoirdupois, but the troy ounce is heavier than the avoirdupois ounce, and the troy pound is lighter than the avoirdupois pound. Legally, one troy ounce (oz t) equals exactly 31.1034768 gram.
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". The word tron refers to markets. Wright's The English Dialect Dictionary lists the word troi as meaning a balance, related to the alternate form 'tron' which also means market or the place of weighing. 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.
Troy weight referred to the Tower system; the earliest reference to the modern troy weights is in 1414.
Many aspects of the troy weight system were indirectly derived from the Roman currency. Before they used coins, Ancient Rome used bronze bars of varying weights as currency. An aes grave ("heavy bronze") weighed one pound. One twelfth of an aes grave was called an uncia, or in English, an "ounce". Before the adoption of the metric system, many systems of troy weights were in use in various parts of Europe, among them Holland troy, Paris troy, etc. Their values varied from one another by up to several percentage points. Troy weights were first used in England in the 15th century and were made official for gold and silver in 1527. The British Imperial system of weights and measures (also known as imperial units) was established in 1824, prior to which the troy weight system was a subset of pre-imperial English units.
The troy ounce in modern use is essentially the same as the British Imperial troy ounce (1824–1971), adopted as an official weight standard for United States coinage by act of Congress on May 19, 1828. The British Imperial troy ounce (known more commonly simply as the imperial troy ounce) was based on, and virtually identical with, the pre-1824 British troy ounce and the pre-1707 English troy ounce. (1824 was the year the British Imperial system of weights and measures was adopted; 1707 was the year of the Act of Union which created the Kingdom of Great Britain.) Troy ounces have been used in England since the early 15th century, and the English troy ounce was officially adopted for coinage in 1527. Before that time, various sorts of troy ounces were in use on the continent.
The troy ounce and grain were also part of the apothecaries' system. This was long used in medicine, but has been largely replaced by the metric system (milligrams). The only troy weight in widespread use is the British Imperial troy ounce and its American counterpart. Both are based on a grain of 0.06479891 gram (exact, by definition), with 480 grains to a troy ounce (compared with grains for an ounce avoirdupois). The British Empire abolished the 12-ounce troy pound in the 19th century. It has been retained, though rarely used, in the American system. 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). 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.
The Dutch troy system is based on a mark of 8 ounces, the ounce of 20 engels (pennyweights), the engel of 32 as. The mark was rated as 3,798 troy grains or 246.084 grams. The divisions are identical to the tower system.
| 373.24172 16 |
| 31.10347 68 |
| 1.55517 384 |
| 0.06479 891 |
The troy system was used in the apothecaries' system but with different further subdivisions.
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