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Pennyweight

physical science Maturity 11-13 Next article →

A pennyweight is a special way to measure mass. We use the short name dwt for this unit. It is mostly used for very valuable things.

Irish pistole
Irish pistole

People use it to weigh precious metals like gold. Jewellers use it to find the cost of metal. They use it when they make or cast jewellery. Dentists also use it for dental crowns and inlays. This helps them measure the metal used in teeth.

Learning how it works is quite interesting. One pennyweight is equal to 24 grains. These grains are part of a troy ounce. A troy ounce is part of a troy pound. You can also link it to an avoirdupois ounce. One pennyweight is exactly 1.55517384 grams. It is a very precise way to measure.

HOARD (FindID 933771-1040559)
HOARD (FindID 933771-1040559)

This helps people know exactly how much metal they have.

This unit has a very long history. In the Middle Ages, an English penny had a specific weight. It was part of a pound of sterling silver. At that time, people used the Tower pound. One pennyweight was then equal to 32 Tower grains. In 1527, the Troy weights replaced the Tower weights. This changed the old Tower pennyweight to 24 Troy grains. This new weight was about 6.667% larger than the old one.

There are many specific facts about this unit. The abbreviation dwt comes from denarius. Denarius was an ancient Roman coin. The abbreviation was also used for an old British penny. In 1878, the United Kingdom passed a new law. The Weights and Measures Act 1878 removed the official status of the pennyweight. However, the troy ounce stayed official in the UK. The troy ounce even has a special legal exemption. This means it is still used in the UK.

You might see this unit in odd places. In Cheshire, UK, people use it for gooseberries. They use pennyweights and grains in fruit competitions. The Egton Bridge Old Gooseberry Society uses different scales. They have used drams and grains since 1937. Do not confuse this with an American penny. A pennyweight is not the same as a one-cent coin. It is also not the same as a penny nail. Those names come from different history.

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