Pennyweight (dwt)

Troy & apothecaries'Traditional unit (still used in some regions)

One twentieth of a troy ounce (1.5552 g), originally the weight of a silver penny. Still used by jewelers.

1 pennyweight = 0.00155517384 kilograms (exactly).

About the pennyweight

Silver pennies gave this unit its name. In the Middle Ages an English penny weighed one twentieth of an ounce and one 240th of a pound of sterling silver, so its weight and its face value agreed. The abbreviation dwt keeps the d from denarius, the Roman coin that stood behind the old British penny.

The size changed over time. Under the medieval Tower pound a pennyweight was 32 Tower grains. When troy weights replaced Tower weights in 1527, it became 24 troy grains, which is exactly 1.55517384 grams.

Twenty pennyweights make a troy ounce, and 240 make a troy pound. Jewellers still use it to work out the precious metal content of jewellery, and dental labs have used it for gold in crowns and inlays. In parts of England, gooseberry growers also record prize fruit in pennyweights and grains.

Sources: Wikipedia: Pennyweight; Wikipedia: Troy weight; NIST SP 811, Appendix B.8

Pennyweight conversion chart

1 pennyweight expressed in every other weight & mass unit:

More Troy & apothecaries' units

• troy ounce (weight & mass)
• troy pound (weight & mass)
• scruple (weight & mass)
• apothecaries' dram (weight & mass)

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