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What is a Troy Ounce?

What is a Troy Ounce?

The Troy ounce is a unit of measurement used specifically for precious metals like gold, silver, platinum, and palladium. It differs from the more common avoirdupois ounce used to weigh everyday items. 

The Troy ounce dates back to the Middle Ages in Troyes, France. It was adopted as the standard measurement for precious metals trading. Today, it remains the key unit for pricing and weighing precious metals in financial markets.

Origins and History

The origins of the troy ounce can be traced back to the 12th century in France. At the Champagne fairs in Troyes, a standard system of weights was used for trading goods. The Troyes system spread through Europe as an accurate set of measurements. 

By the 14th century, the troy ounce became the standard unit of measure for precious metals like gold and silver. It was larger than other ounce variants which made it well-suited for weighing small quantities of dense, high-value metals.

The British Empire eventually adopted the Troy system. In the late 19th century, Troy weights were made the legal standard for monetary precious metals in England. Today, Troy ounces are still used in British coinage and international precious metal markets.


The Troy ounce is a unit of measurement used specifically for precious metals like gold, silver, platinum, and palladium. It differs from the more common avoirdupois ounce used to weigh everyday items.


Differences from Avoirdupois Ounce

The Troy ounce is approximately 10% heavier than the Avoirdupois ounce used for most other weights. One Troy ounce equals 31.1034768 grams. An Avoirdupois ounce is 28.349523125 grams. 

This difference makes the troy ounce more precise for weighing small amounts of precious metals. Precious metals are traded and priced by the Troy ounce rather than the Avoirdupois ounce.

Usage in Precious Metal Markets

The Troy ounce continues to be the pricing unit for precious metals like gold, silver, and platinum. Commodity exchanges like the London Bullion Market trade metals using the Troy ounce. Prices of precious metals are almost universally quoted in USD or other currencies per Troy ounce.

The Troy system also includes other specialized weight measurements for precious metals. These include the pennyweight, used by jewellers, and the grain, used for very small amounts.

In addition, the purity of gold and other metals is measured in carats, which represent 1/24th divisions of pure gold by weight.