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Sovereign Gold & Silver Exchange
A bullion label can show a weight, a purity and a denomination, all on the same small piece of metal. Those numbers answer different questions. Learning to separate them makes it easier to understand a product description before you compare prices.
An ounce is not always the same ounce
Precious metals are commonly measured in troy ounces. One troy ounce is approximately 31.10348 grams. The everyday ounce, called the avoirdupois ounce, is approximately 28.34952 grams. They are not interchangeable. These conversions come from the National Institute of Standards and Technology. [1]
For a quick conversion, divide grams by 31.10348 to obtain troy ounces. For example, 10 grams is about 0.3215 troy ounce, not one-third of a troy ounce. This calculation converts a weight only. It does not tell you the item's purity or whether the stated weight describes the whole item or its precious-metal content.
When a listing simply says “oz,” look for the issuer's specifications rather than guessing which unit it means.
Total weight and fine weight answer different questions
Gross weight is the weight of the metal item as a whole, including alloying metals. Fine gold weight is the amount of gold it contains. To calculate fine gold from a known gross weight, multiply that weight by the gold purity expressed as a decimal. LBMA illustrates this distinction in its precious-metals market definitions. [2]
Here is a hypothetical example, not a product offer: an item weighing 100 grams at 90% gold contains 90 grams of gold. That is about 2.8936 troy ounces of fine gold. The other 10 grams are not gold.
Keep the units consistent throughout the calculation. Also check whether a product's stated weight is already its fine-metal content. If it is, multiplying it by the purity again would incorrectly reduce the amount a second time.
Why a one-ounce Gold Eagle weighs more than one troy ounce
The American Eagle one-ounce gold bullion coin provides a useful real example. The U.S. Mint lists its total weight as 33.931 grams, or 1.0909 troy ounces, and its composition as 91.67% gold, 3% silver and the balance copper. It contains its stated one troy ounce of gold, plus alloying metals. [3]
There is no contradiction between the one-ounce name and the heavier total weight. One describes the gold content; the other includes the alloy. Use the Mint's stated gold content rather than expecting rounded specification figures to reproduce every last decimal in a calculation.
A short checklist before comparing products
Ask four questions:
- What is the exact coin or bar, including its size and version?
- Is the weight stated in grams or troy ounces?
- Does that weight mean the whole metal item or its fine-metal content?
- Where does the issuer document the purity and metal content?
Keep that description with your records. A weight conversion explains quantity, not authenticity, condition or the full selling price. For a broader starting point, read our guide to buying your first gold or silver.
The useful habit is simple: identify the unit, identify what is being weighed, and compare like with like.
Sources
- NIST, Guide to the SI, Appendix B.9, Mass and Moment of Inertia
- LBMA, Annex 3: Precious Metals Basic Market Definitions
- U.S. Mint, Bullion Coin Programs: American Eagle Gold Bullion Coins
Photo: “Gold Coins” by frankieleon, CC BY 2.0. Image unaltered. Illustrative photograph, not SGSE inventory.
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