The troy ounce is the standard unit of measurement for precious metals (gold, silver, etc.) and gemstones. This is an important fact for the precious metals investor to keep in the memory bank, for the simple reason that it is different from what we call an ounce in everyday life. Although this distinction will never arise as an issue when you purchase or sell bullion products here at Goldbroker.com, it could be a concern elsewhere and we will get to that later.
The troy weight system pre-dates the metric system, as well as America’s commonly-used avoirdupois system in which an ounce means an ounce, 16 of which make up a pound. The troy and avoirdupois systems share the same basic legal unit: the grain. This harks all the way back to the Bronze Age, when the measurement of mass was based on a single seed of a cereal plant such as wheat or barley. Variations in weight between plant species and even same species created obvious discrepancies. Finally, the issue became subject to modern formalization in 1959 under the International Yard and Pound Agreement, and that is the foundation of our weight system: 7,000 grains make up one avoirdupois (American) pound. But … there are only 5,760 grains in a troy pound.
Conclusion: A troy grain is heavier than an avoirdupois grain and, therefore, the troy ounce is heavier than the common American ounce.
(Before we leave the tiny realm of the grain, gun experts may recognize it as the unit of measurement for the mass of bullets and propellants, reflecting the value placed on ammunition in world history, on par with that of gold and silver wealth. A single particle of gunpowder is also known as a grain. Furthermore, although rarely ever used anymore, weights in the apothecaries’ system are equivalent to those of the troy system: a standard aspirin tablet contains 5 grains.
One other word before we get down to strictly useful business, and it concerns the troy pound. This is tricky business because, although the troy ounce is heavier than the avoirdupois ounce, the troy pound is lighter than the avoirdupois pound. This is because, in troy measurement, there are 12 ounces to a pound, compared to the American 16 ounce pound that you see represented on your grocery packages and (gulp) bathroom scales. This is interesting to know but somewhat irrelevant, however, as the troy pound is not used as a benchmark in precious metals or any other known commodity.
The troy ounce is equal to 31.1035 grams, about 10% more (2.754 grams) more than the avoirdupois ounce which weighs in at 28.3495. The difference is just under one tenth of one ounce. That may seem like a tiny disparity but bear in mind that the United States Mint strikes a tenth-ounce Gold American Eagle coin that is roughly the size of your thumbnail. Many (if not most) other mints around the world do likewise, to the unending delight of collectors everywhere.
1 troy ounce = 31.1035 grams or 480 grains
1 ounce = 28.3495 grams or 437.5 grains
The small variance becomes significant to bullion investors. For instance, Goldbroker.com offers you a selection of 1 Kilogram gold bars as an excellent avenue to the acquisition of the highest-quality gold at close to spot price. At this level, the difference between the weight systems equates to more than 10 full ounces on conversion from the metric. The stakes rise exponentially once you get to Good Delivery bars. Designated as such according to rules established by the London Bullion Market Association, these are used in the major international markets (New York, Zurich, Sydney, Hong Kong, Tokyo and London) and in the gold reserves of governments, central banks and the International Monetary Fund. Good Delivery gold bars weigh 400 troy ounces, while those in silver weigh 1000 troy ounces.
Now you have all the necessary information. And here is your word of caution: If you are ever offered gold or silver or any precious metal for sale, remember what you have read here and make sure it is measured in troy ounces. If you buy in common ounces, you will be paying approximately 10% more than actual worth, in troy ounces. In short, do not buy gold in avoirdupois weight.
Goldbroker.com provides the weights of all its products in troy ounces.