What is the difference between a troy ounce and regular ounce?

It is the industry standard for bullion to be weighed and priced according to troy ounces. A troy ounce is slightly heavier than a regular ounce. One troy ounce is equal to 1.09714 avoirdupois ounces.

The troy weight system was used throughout much of Europe before the metric system. This system can be traced back to the Roman monetary system, where 1-pound bronze bars were used as currency. A bronze bar would be divisible by 12, with each piece called “uncia” or ounce, weighing around 31.1 grams. As Europe became the hub for international trade in the 10th century, a standardized monetary system became a necessity. Historians believe the name “Troy” is linked to the market town Troyes, France, where merchants would meet to trade goods.