In the Middle Ages, an English penny's weight was literally, as well as monetarily, of an ounce and of a pound of sterling silver. At that time, the pound unit in use in England was the Tower pound, equal to 7,680 Tower grains. The medieval English pennyweight was thus equal to 32 Tower grains. When Troy weights replaced Tower weights in 1527, the Troy weights were defined in such a way that the old Tower pound came out to exactly 5,400 Troy grains, the Tower pennyweight Troy grains. After 1527, the English pennyweight was the Troy pennyweight. of 24 Troy grains. Thus the Troy pound, ounce, and pennyweight, with their definitions given in terms of the Troy grain instead of in terms of the Tower grain, were or 6.667% more than the Tower equivalents.
Usage
The troy pound and the pennyweight lost their official status in the United Kingdom in the Weights and Measures Act of 1878; only the troy ounce and its decimal subdivisions remained official. The troy ounce enjoys a specific legal exemption from metrication in the UK. The pennyweight is the common weight used in the valuation and measurement of precious metals. Jewellers use the pennyweight in calculating the amount and cost of precious metals used in fabricating or casting jewellery. Similarly, dentists and dental labs still use the pennyweight as the measure of precious metals in dental crowns and inlays. Pennyweight and grains are still used to weigh gooseberries in competitions in Cheshire, northwest UK. Over the Pennines in Yorkshire the alternative drams and grains measurement has been used since a new set of scales was purchased by the Egton Bridge Old Gooseberry Society in 1937. As of 2018, the world record for the heaviest gooseberry of was held by Kelvin Archer of Cheshire. The most common abbreviation for pennyweight is dwt; d, for the Roman denarius, was the abbreviation for penny before Decimalization of the British monetary system. Alternate abbreviations are pwt and PW.
Uses unrelated to weight
Although the abbreviations are the same, the pennyweight bears no relation to the weight of the Americanpenny nail. That name is derived from the price for a hundred nails in 15th century England: the larger the nail, the higher the cost per hundred. The pennyweight also bears no relation to the weight of the American "penny" coin, which weighs 2.5 g.
