Ounce-Gram Weight 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 inevitably encounters two different weight units: the price per troy ounce quoted on exchanges, and the everyday gram. Converting between them is simple - but only if you know which "ounce" is meant. The unit converter converts any unit in seconds.
The troy ounce - not to be confused with the trade ounce
In precious-metal trading, only the troy ounce applies (abbreviated ozt or oz t). It descends from the medieval troy weight system, which originated in the English (and French) city of Troyes, and was established by the LBMA as the binding pricing unit.
Alongside it exists the avoirdupois ounce (oz av), used in everyday Anglo-American commerce for food, post and other goods. It is lighter than the troy ounce:
| Unit | Grams | Use |
|---|---|---|
| Troy ounce (ozt) | 31.1034768 g | Precious metals worldwide |
| Avoirdupois ounce (oz av) | 28.3495 g | Everyday use (USA, UK) |
| Difference | +2.754 g | The troy ounce is heavier |
Anyone who inadvertently calculates with the avoirdupois ounce underestimates the amount of metal by almost 9.7% - a significant error when buying or selling.
Conversion formulas
Grams -> troy ounces: g / 31.1034768 = ozt
Troy ounces -> grams: ozt x 31.1034768 = g
Handy reference values for quick mental arithmetic:
- 1 ozt approx. 31.1 g (sufficient for rough estimates)
- 10 ozt approx. 311 g (e.g. ten 1 ozt silver coins)
- 1 kg = 32.1507 ozt (relevant for kilo bars)
- 100 g = 3.2151 ozt (a common bar denomination)
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 17th century, COMEX in New York since its founding in 1933, and the LBMA as a formal institution since 1987. All global reference prices, ETF valuations, futures contracts and central-bank reserves are based on this unit. Switching would require a complete redesign of every international trading standard and is regarded as 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 |
With the melt value calculator you only need to enter the weight in grams - the conversion to troy ounces and the multiplication by the current spot price happen automatically.
Fine weight vs. gross weight
Important: the weight of a coin or bar in grams is the gross weight (total weight including alloy content). The fine weight - the amount of pure metal it contains - is obtained only by multiplying by the fineness:
Fine weight (g) = gross weight (g) x fineness (e.g. 0.999)
A Krugerrand (22 carat, fineness 916.7) weighs around 33.93 g gross, but contains exactly 1 ozt = 31.1035 g of fine gold. The difference is the copper added to the alloy.
In brief
The troy ounce, at exactly 31.1034768 grams, is the indispensable bridging unit between the international exchange price and the weight in your hand. Anyone who fails to keep the gram and the avoirdupois ounce cleanly apart is calculating at odds with the market. The unit converter makes this distinction automatically.