Pennyweight 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" (1 cent) coin, which weighs 2.5 g (for those minted after 1982). Pennyweight A pennyweight (abbreviated dwt, from denarius weight) is a unit of mass that is equal to 24 grains, of a troy ounce, of a troy pound, approximately 0.054857 avoirdupois ounce and exactly 1.55517384 grams. In the Middle Ages, a British penny's weight was literally, as well as monetarily, of an ounce
Exchequer Standards inches. According to Secretary Adams, Adams goes on to say (paraphrased and simplified): Thus, the key to the whole measurement system of 1266 was the weight of the silver penny sterling. This penny was 1/240th of the Tower pound, which had been used at the London mint for centuries before the Norman conquest, and which continued as legal tender until 1527, when Henry VIII replaced it with the Troy pound. The Tower pound weighed 3/4 Troy ounce less than the Troy pound (15/16th of the Troy pound). Its penny, therefore weighed 22.5 Troy grains. There was also another pound used