Troy weight
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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). 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 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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Troy pound
The troy pound (troy) is 5,760 gr (≈ 373.24 g, 12 ozt), while an avoirdupois pound is heavier at 7,000 gr (≈ 453.59 g).
Troy ounce
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. The 'd' in dwt is for denarius, the ancient Roman coin equivalent to a penny.
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 | 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 | 147⁄12 | 155⁄9 | 7000 | ~454 | ~9⁄20 |
| Troy | 144⁄175 | 1 | 16⁄15 | 64⁄75 | 4⁄5 | ~3⁄4 | 1329⁄175 | 12 | 124⁄5 | 5760 | ~373 | ~3⁄8 |
| Tower | 27⁄35 | 15⁄16 | 1 | 4⁄5 | 3⁄4 | ~7⁄10 | 1212⁄35 | 111⁄4 | 12 | 5400 | ~350 | ~7⁄20 |
| Merchant | 27⁄28 | 75⁄64 | 5⁄4 | 1 | 15⁄16 | ~7⁄8 | 153⁄7 | 141⁄16 | 15 | 6750 | ~437 | ~7⁄16 |
| London | 36⁄35 | 5⁄4 | 4⁄3 | 16⁄15 | 1 | ~14⁄15 | 1616⁄35 | 15 | 16 | 7200 | ~467 | ~7⁄15 |
| Metric | ~11⁄10 | ~4⁄3 | ~10⁄7 | ~8⁄7 | ~15⁄14 | 1 | ~173⁄5 | ~16 | ~171⁄7 | ~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
References
External links
- History of the Troy Ounce
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