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. The Troy weight system was standardized by Henry II of Britain during his reign in the 12th century. At that time a silver penny weighed 1 DWT. (pennyweight = 1.55 grams AV), 12 pennies made a shilling and 20 shillings made a British pound (£), so a pound sterling weighs 240 DWT. just the same as it did a thousand years ago!
A Troy ounce (ozt) is 480 grains, about 10% heavier than an avoirdupois ounce (437.5 grains). A grain is exactly 64.79891 mg; hence one troy ounce is exactly 31.1034768 grams, about 10% more than the avoirdupois ounce, which is exactly 28.349523125 grams. The troy ounce is traditionally used over the avoirdupois ounce 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. The grain is also common to the apothecaries system and was long used in medicine, but has been largely replaced by milligrams (mg).
Pennyweight (dwt): 24 grains = 1 dwt (1.555 grams av) 20 dwt = 1 troy ounce (31.1 g av)
Troy pound: 5760 grains = 240 dwt = 12 ozt = 1 troy pound
5760 grains = 12 ozt = 1 troy pound 7000 grains = 16 oz = 1 lb avoirdupois
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A US penny has nothing to do with a pennyweight and is heavier (1.61 grams) so do not use Lincoln pennies to weigh your jewelry. You may use a kitchen scale or postage scale to weigh it in grams. Divide the gram weight by 1.55 to convert grams to DWT. This will give you a pretty good idea of how many DWT. you have to sell. Our scales are electronic and are sensitive to 1/1000th of a gram so your estimate and the actual settlement weight will vary some. A DWT. is a very small amount of gold BUT as you can see, its worth its weight in gold!