pennyweight

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A pennyweight (abbreviated dwt) is a unit of mass that is equal to 24 grains, 1/240 of a troy pound, 1/20 of a troy ounce, approximately 0.055 ounces^{[clarification needed]}, and approximately 1.555 grams.

Historically, a British penny's weight was literally, as well as monetarily, 1/240 of a troy pound of sterling silver. The troy pound and the pennyweight lost their official status in the United Kingdom of Great Britain and Ireland in the Weights and Measures Act of 1878. Only the troy ounce and its decimal subdivisions remained official after the 1878 act. 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 jewelry. Similarly, dentists and dental labs still use the pennyweight as the measure of precious metals in dental crowns and inlays.

The most common abbreviation for pennyweight is dwt; d, for the Roman denarius, was the abbreviation for penny before decimalisation of the British monetary system. Alternate abbreviations are pwt and PW.

The pennyweight bears no relation to the weight of current penny coins. The weight of a US penny since 1982, for example, is 2.5 grams.^[1]

Notes

1. ^ http://www.usmint.gov/about_the_mint/index.cfm?action=coin_specifications