What is a Troy ounce?

When you buy or sell precious metals such as gold, silver or platinum, you usually buy or sell them by their weight. For instance, as well as a variety of other bars, we currently offer a one-ounce gold bar. If you scroll down to look at its specifications, you will see that against its weight, it states one troy or 31.21g.

Here in the UK, before we adopted the metric system, we used and still do to some extent, a system called the avoirdupois system. The name comes from Anglo-Norman French and means ‘goods of weight’. It is based on pounds and ounces and there are 16 ounces to a pound.

However, around medieval times when traders were bartering for goods, all precious metals were weighed using the troy system, not the avoirdupois system. The troy system uses pounds and ounces, so it is similar, but there is one big difference; there an avoirdupois ounce equals 28.35 grams, whereas a troy ounce weighs 31.10 grams. This means one troy ounce is equivalent to approximately 1.09714 avoirdupois ounces. We still use the troy system today, especially when weighing precious metals.

Do precious metal weights differ in other countries?

Other countries have various systems for weight, and they differ in the number of grams there are depending on the country. For example, in North America they have the Pennyweight, which they use to weigh precious metals - it is equal to 1/20 of a troy ounce.

In South East Asia, China and Hong Kong, a system called the Tael, or Tahil is used. The Tahil has different weights depending where it is used. In China, one Tahil is equal to 50 grams, whereas in Japan it is 37.5 grams, so there is quite a difference.  In Thailand, they use the Bhat, which is equal to 15.244 grams.

In places like Karachi, New Delhi, Pakistan, Mumbai, Singapore and Nepal, they use the Tola system for weighing gold. Tola means weight and the name has its roots in Sanskrit. It weighs 3/8 of a troy ounce, or 180 grains.

Grains of wheat were traditionally used as weights by measuring the grain from dried kernels. It is the smallest unit of weight used in troy and avoirdupois systems. Jewellers used to use a system called the Jewellers Grain to measure precious stones before the use of the carat came into being. A Jewellers Grain is equal to one quarter of a carat.

Buying precious metals from The Royal Mint

Any coins you buy from The Royal Mint will give you the details of the amount of a particular precious metal in the coin. For example, The Sovereign gold bullion coin weighs 0.2354 troy ounces, whilst the Half Sovereign coin weighs 0.1407 troy ounces.

The Royal Mint also sells gold, silver and platinum bars. They come in various weights and sizes and are another popular way to invest in precious metals.

Furthermore, The Royal Mint’s digital offering DigiGold provides another convenient way to invest in precious metals. DigiGold enables you to buy gold, silver or platinum by value, rather than weight, giving you the flexibility to buy a fraction of a large 400 oz. bar for a minimum of £25. The bars are kept securely in The Vault at The Royal Mint, and you are able to buy, store and sell at your convenience.

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