Precious metal units of measure explained

The precious metals industry uses the troy ounce as its basic unit of measure, even in countries who have adopted the metric system. A troy ounce is heavier than the more common avoirdupois ounce.

While there is a difference between a troy ounce and an ounce, the precious metals industry often uses “ounce” and the abbreviation “oz” rather than “troy ounce” and “ozt”. As a result, when you see “ounce” and “oz” used in the context of precious metals, assume the reference is to troy ounces.

When referring to large quantities (such as annual mine production), the industry often uses metric tonnes as the unit of measure as it produces smaller and more manageable numbers. For example: 80,376,867 troy ounces equals 2,500 tonnes. Some prefer to use “millions of ounces” (abbreviated to “moz”) to avoid confusion as to whether the “ton” referred to is a metric ton, Imperial (long) ton or US (short) ton. For silver, traders can use the Indian unit of measure Lakh (or Lac) which refers to 100,000. For example, a trade for 1,000,000oz would be referred to as 10 Lakh.

Precious metal weights are usually only recorded to three decimal places of accuracy, or to one thousandths of an ounce. An exception to this is a gold London Good Delivery Bar, which is rounded down to the nearest 0.025 of a troy ounce (silver London Good Delivery Bars are rounded down to the nearest 0.100 of a troy ounce).

The tables below list conversion rates between a troy ounce and other common units of mass, with abbreviations in brackets.

Imperial/US

Metric

Other