Units of Measure for Precious Metals
The precious metals industry uses the troy ounce as its basic unit of measure, even in countries that have adopted the metric system. A troy ounce is heavier than the more common avoirdupois ounce. The tables below list conversion rates between a troy ounce and other common units of mass, with abbreviations in brackets.
Imperial | US
| 1 troy ounce (ozt) = 480 grains | 1 grain (gr) = 0.00208333 troy ounces |
| 1 troy ounce (ozt) = 1.097142794 ounces | 1 ounce (oz) = 0.91145839 troy ounces |
| 1 troy ounce (ozt) = 20 pennyweights | 1 pennyweight (dwt) = 0.05 troy ounces |
| 1 troy ounce (ozt) = 0.0685714246 pounds | 1 pound (lb) = 14.58333418 troy ounces |
| 1 troy ounce (ozt) = 0.00003061224 tons (I) | 1 ton Imperial (t) = 32666.67189333 troy ounces |
| 1 troy ounce (ozt) = 0.0000342857123 tons (US) | 1 ton US (t) = 29166.66835590 troy ounces |
Metric
| 1 troy ounce (ozt) = 31.1034768 grams | 1 gram (g) = 0.032150746568628 troy ounces |
| 1 troy ounce (ozt) = 0.0311034768 kilograms | 1 kilogram (kg) = 32.150746568628 troy ounces |
| 1 troy ounce (ozt) = 0.0000311034768 tons | 1 ton (t) = 32150.746568628 troy ounces |
Other
| 1 troy ounce (ozt) = 0.375 toal | 1 tola = 2.66666667 troy ounces |
| 1 troy ounce (ozt) = 0.83099941 tael | 1 tael = 1.20337029 troy ounces |
| 1 troy ounce (ozt) = 0.08333333 troy pounds | 1 troy pound = 12 troy ounces |
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 1,000,000 oz would be referred to as 10 Lakh.
Precious metal weights are usually only recorded to three decimal places of accuracy, or to one one-thousandth 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).
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Interesting. I also write “oz.” next to the ASW of my coins. I should be writing ozt, which is more accurate. I forgot about that! Thanks