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, at the celebrated fair at Troyes in North Eastern France. 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).[1] There are 12 troy ounces per troy pound,[2] rather than 16 avoirdupois ounces (oz) in the avoirdupois pound (lb) as in the more common avoirdupois system. The avoirdupois pound is 147⁄12 (≈ 14.583) troy ounces. Although Troy Ounces are still used to weigh gold, silver and gemstones, the Troy Pound is no longer used.
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Units of measurement
- Troy pound (troy)
The troy pound (troy) is 5,760 grains (≈ 373.24 g, 12 ozt), while an avoirdupois pound is heavier at 7,000 grains (≈ 453.59 g).
- Troy ounce (ozt)
One troy ounce (ozt) is equal to 31.1034768 grams.
- Pennyweight (dwt)
The pennyweight symbol is dwt. There are 24 grains in 1 dwt, and 20 dwt in one troy ounce. Because there were 12 troy ounces in the old troy pound, there would have been 240 pennyweights to the pound—the basis of the fact that the old British pound (currency) contained 240 pence. (However, prior to 1526, English pound sterling was based on the tower pound, which is 15/16 of a troy pound.) The d in dwt stands for denarius, the ancient Roman coin, referred to in the New Testament, that equates loosely to a penny. The symbol d for penny can be recognized in the old-style notation for British pennies, in which a quantity of money expressed in pounds, shillings, and pence was indicated using the symbols £, s, and d, respectively. For example, £6.11s.8d indicated six pounds, eleven shillings, and eight pence.
- Troy grain
Scottish system
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.
Conversions
| Unit | Grains | Grams |
|---|---|---|
| Troy pound (12 troy ounces) | 5,760 | 373.241 721 6 |
| Troy ounce (20 pennyweights) | 480 | 31.103 476 8 |
| Pennyweight | 24 | 1.555 173 84 |
| Grain | 1 | 0.064 798 91 |
| Unit | Pounds | Ounces | Grains | Metric | ||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| avdp. | troy | tower | merc. | lond. | metric | avdp. | troy | tower | g | kg | ||
| Avoirdupois | 1 | 175⁄144 | 35⁄27 | 28⁄27 | 35⁄36 | 10⁄11 | 16 | 14 7⁄12 | 15 5⁄9 | 7000 | 454 | 9⁄20 |
| Troy | 144⁄175 | 1 | 16⁄15 | 64⁄75 | 4⁄5 | 3⁄4 | 13 29⁄175 | 12 | 12 4⁄5 | 5760 | 373 | 3⁄8 |
| Tower | 27⁄35 | 15⁄16 | 1 | 4⁄5 | 3⁄4 | 7⁄10 | 12 12⁄35 | 11 1⁄4 | 12 | 5400 | 350 | 7⁄20 |
| Merchant | 27⁄28 | 75⁄64 | 5⁄4 | 1 | 15⁄16 | 7⁄8 | 15 3⁄7 | 14 1⁄16 | 15 | 6750 | 437 | 7⁄16 |
| London | 36⁄35 | 5⁄4 | 4⁄3 | 16⁄15 | 1 | 14⁄15 | 16 16⁄35 | 15 | 16 | 7200 | 467 | 7⁄15 |
| Metric | 11⁄10 | 4⁄3 | 10⁄7 | 8⁄7 | 15⁄14 | 1 | 17 3⁄5 | 16 | 17 1⁄7 | 7716 | 500 | 1⁄2 |
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.
See also
- Carat (unit)
- Conversion of units
- Mark (weight)
References
- ↑ Wightman, S.; Blanchard, William (1840). Wightman's Arithmetical Tables. Westminster: S. Wightman. OCLC 43196919.
- ↑ "Troy Ounce". WordNet 3.0, Dictionary.com. Princeton University. http://dictionary.reference.com/browse/troy%20ounce. Retrieved 2008-01-10.
External links
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