The fact that gold bullion is weighed in troy ounces reflects its ancient heritage as a treasured commodity. During the 12th and 13th centuries, trade fairs flourished in Champagne, which is now part of northeastern France. One of the region’s key cities is Troyes, from which “troy” ounce is derived. Since the time of the Champagne trade fairs, the troy ounce and its ancient denominations, the grain and the pennyweight, have been used for weighing precious metals. One grain was equivalent to the weight of a grain of wheat, 24 grains equaled a pennyweight, and 20 pennyweights made up a troy ounce. During the reign of King Henry VIII in 1527, the annual test of England’s coinage, known as the Trial of the Pyx, included a ruling that the troy pound, consisting of 12 troy ounces, would be the basis of measurement for gold and silver.
By the 19th century, with the advent of the metric systems, the troy ounce could be defined far more precisely. It is equivalent to 31.103 grams. Importantly, the troy ounce is about 10 percent heavier than a standard ounce, known as an avoirdupois ounce, which weighs 28.349 grams.
To this day, gold, silver, platinum, and palladium are still weighed in troy ounces, which maintains historical continuity and global consistency for these treasured precious metals.
