US Coins

An ounce of gold, like in this 1-ounce gold American Eagle, weighs more than an ounce of feathers. Gold is measured in troy ounces (each equal to 31.1 grams); feathers are measured in avoirdupois ounces (28.35 grams each).

Coin World file image.

An old mind teaser asks, “Which is heavier, a pound of lead or a pound of feathers?”

Would the answer be the same if the feathers were compared with gold? The “Ship of Gold” article in the Coin World Extra accompanying the May Coin World Special Edition mentioned the Eureka bar weighing “933.94 ounces ... nearly 80 pounds.”

This seems to confirm the information I have heard, which is that a pound of gold contains just 12 ounces. Can you confirm that a pound of gold is in fact only 12 ounces, and if so, the origin of this seeming oddity. Are the ounces and pounds avoirdupois weight?

Perhaps asked another way, how many grams are in an ounce and in a pound of gold?

Randy Vodney

Jacksonville, Fla.

Precious metals such as gold and silver, and gemstones, are measured in troy ounces. Everyday measurements (food, copper, your body weight) are measured in avoirdupois ounces. A troy ounce (12 to a troy pound) is about 10 percent heavier than an avoirdupois ounce (16 to an avoirdupois pound). When converted metrically, a troy ounce weighs 31.1 grams and an avoirdupois ounce is equal to 28.35 grams.

The term “troy” appears to have its origins in the Middle Ages in the town of Troyes in northern France, with the first use of the word recorded in 1390. The troy system itself was actually a series of closely related weight systems in use in Europe, bearing such names as the Bremen troy and the Paris troy, as used in those cities.

Upon the adoption of the metric system, first by France in 1799 and gradually internationally, a troy ounce was standardized. Britain adopted a British imperial troy ounce in 1824, at 31.1034768 grams, and the United States adopted that standard in 1828. In 1959, by international agreement, a troy ounce was officially established as weighing 31.1034768 grams.

Historically, the troy weight system was indirectly derived from Roman coinage. The Roman aes grave, or a heavy bronze coin, was equal to a pound, which was divisible into 12 unciae or ounces (an uncia was also used as an unit of measurement roughly equal to a modern inch). Eventually, the ounce was standardized to 16 per pound under the avoirdupois system.

However, according to various sources, precious metals continued to be measured by troy ounces in order to maintain historical purity standards and common measurements. An ounce of gold in 1799, for example, would be equal to an ounce of gold today.

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