Ounce-Gram Conversion
Also: Ounce to grams, oz to g, Troy ounce conversion, ozt
The troy ounce is the international standard unit for precious metal prices and equals exactly 31.1034768 grams.
Anyone following precious metal prices soon runs into two different units of weight: the exchange-quoted price per troy ounce and the everyday gram. Converting between the two is simple - but only once you know which "ounce" is meant. The unit converter turns any unit into another in seconds.
The troy ounce - not to be confused with the everyday ounce
In the precious metal trade only the troy ounce applies (abbreviated ozt or oz t). It descends from the medieval troy weight system that originated in the French town of Troyes, and the LBMA fixed it as the binding pricing unit.
Sitting alongside it is the avoirdupois ounce (oz av), used in the Anglo-American world for food, post and general goods. It is lighter than the troy ounce:
| Unit | Grams | Used for |
|---|---|---|
| Troy ounce (ozt) | 31.1034768 g | precious metals worldwide |
| Avoirdupois ounce (oz av) | 28.3495 g | everyday goods (US, UK) |
| Difference | +2.754 g | the troy ounce is heavier |
Reach mistakenly for the avoirdupois ounce and you underestimate the amount of metal by nearly 9.7% - a serious error when buying or selling.
Conversion formulae
Grams to troy ounces: g / 31.1034768 = ozt
Troy ounces to grams: ozt x 31.1034768 = g
Handy figures for quick mental arithmetic:
- 1 ozt ~ 31.1 g (good enough for rough estimates)
- 10 ozt ~ 311 g (say, ten 1 ozt silver coins)
- 1 kg = 32.1507 ozt (relevant for kilo bars)
- 100 g = 3.2151 ozt (a common bar size)
Why is the troy ounce still the standard?
The gold price and the silver price have been quoted in troy ounces for centuries - the London gold market has used the unit since the seventeenth century, COMEX in New York since its founding in 1933, and the LBMA as a formal body since 1987. Every global reference price, ETF valuation, futures contract and central bank reserve rests on this unit. Switching would demand a complete redesign of all international trading standards, and is considered unrealistic.
Conversion for common coin and bar sizes
| Product | Nominal weight (ozt) | Actual weight (g) |
|---|---|---|
| Standard bullion coin | 1 ozt | 31.1035 g |
| Half ounce | 0.5 ozt | 15.5517 g |
| Quarter ounce | 0.25 ozt | 7.7759 g |
| Tenth ounce | 0.1 ozt | 3.1103 g |
| Small bar | 1 g | 0.03215 ozt |
| Bar | 5 g | 0.16075 ozt |
| Bar | 10 g | 0.32151 ozt |
| Bar | 100 g | 3.21507 ozt |
| Kilo bar | 1,000 g | 32.1507 ozt |
At the melt value calculator it is enough to enter the weight in grams - the conversion to troy ounces and the multiplication by the current spot price happen automatically.
Fine weight versus gross weight
An important point: a coin's or bar's weight in grams is the gross weight (the total, including any alloying metals). The fine weight - the amount of pure metal it actually contains - only emerges when you multiply by the fineness:
Fine weight (g) = gross weight (g) x fineness (e.g. 0.999)
A Krugerrand (22 karat, fineness 916.7) weighs about 33.93 g gross, yet contains exactly 1 ozt = 31.1035 g of fine gold. The difference is the copper in the alloy.
In a nutshell
The troy ounce, at exactly 31.1034768 grams, is the indispensable bridge between the international exchange price and the weight in your hand. Fail to keep the gram and the avoirdupois ounce cleanly apart and you will be trading past the market. The unit converter draws that distinction for you automatically.