Troy Ounce

A troy ounce is a unit of measure used for weighing precious metals that dates back to the Middle Ages. Originally used in Troyes, France, one troy ounce is equal to 31.1034768 grams, according to the UK Royal Mint. One standard ounce (also known as the Avordupois ounce) is instead used to weigh other commodities such as sugar and grain, and is slightly less at 28.35 grams.

The troy ounce is retained even today as the standard unit of measurement in the precious metals market to ensure purity standards and other common measures remain consistent over time. The troy ounce is often abbreviated to read "t oz" or "oz t."

The troy ounce is the only measure of the troy weighting system that is still used in modern times. It is used in the pricing of metals, such as gold, platinum, and silver. Thus, when prices of precious metals are listed per-ounce, it is often referencing the troy ounce.

It was also used when weighing certain gemstones. The troy weight system, however, has largely been replaced by the carat system in the world of precious gems and stones.

The troy system for weights and measures is thought to originate from the middle-ages French city of Troyes, a mercantile hub that attracted merchants from around Europe and Britain. In Troyes, merchants measured 480 grains of barley to equal a troy ounce, and 12 troy ounces equaled one troy pound.

Some historians believe the troy ounce had its origins in Roman times. Romans standardized their monetary system using bronze bars that could be broken down into 12 pieces called "uncia" or ounce, with each piece weighing around 31.1 grams. As Europe's economic importance grew from the 10th century onward, merchants came from all over the world to buy and sell goods there. It was, therefore, necessary to develop a new standardized monetary weight system to make doing business much easier. Some believe the merchants of Troyes modeled this new monetary system using the same weights as their Roman ancestors.

Before the adoption of the metric system across Europe, the French-born King Henry II of England adjusted the British coinage system to be more reflective of the French troy system. The system was adjusted periodically, but troy weights, as we know them today, were first used in England in the 15th century.

Prior to the adoption of the troy system, the British used an Anglo-Norman French system called the avoirdupois system, which means "goods of weight" and was also used to weigh both precious metal and non-precious metal items. By 1527, the troy ounce became the official standard measurement for gold and silver in Britain, and the US followed suit in 1828.

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