The pennyweight was the weight of a silver penny in medieval England. When pennies were introduced in England in the 8th century, their original weight is believed to have been 24 grains. This was gradually reduced, in at least thirteen stages until it reached 7.27 grains by 1816.
According to one knowledgeable source, the pennyweight was introduced by Henry III in 1266 as the weight of 32 grains of wheat. We believe this may simply have been clarifying and codifying an existing standard.
24 grains = 1 pennyweight
20 pennyweights = 1 ounce troy
240 pennyweights = 1 pound troy
It is no coincidence that there were 240 pennies to the English pound , and 240 silver pennies were equivalent to a pound of silver, or that the word sterling applies both to the english pound and to a standard purity of silver.
Please see our longer page about other weights used for gold, other precious metals, jewellery and gemstones.