Gold: Converting Grams to Troy Ounces and Pounds
Precious metals use a different ounce from everything else. Getting the two mixed up misstates a quantity by nearly ten percent.
To convert gold from grams to troy ounces, divide the grams by 31.1034768. One troy ounce is exactly 31.1034768 grams, so 100 grams of gold is 3.215 troy ounces. Using the ordinary ounce of 28.349523125 grams instead would give 3.527, which overstates the quantity by 9.71 percent.
The quick answer
Divide grams by 31.1034768 for troy ounces, and by 453.59237 for ordinary pounds. Gold, silver, platinum and palladium are quoted in troy ounces almost everywhere in the world, so the troy figure is the one that matters for pricing. A 100 gram bar is 3.215 troy ounces and 0.2205 ordinary pounds.
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Troy weight against ordinary weight
A troy ounce is heavier than an ordinary ounce: 31.1034768 grams against 28.349523125 grams, a difference of about 2.75 grams. The ordinary ounce is properly called the avoirdupois ounce and is the one used for food, parcels and body weight. Troy weight survives from the medieval bullion trade and is now used almost exclusively for precious metals and gemstones.
The confusing part is that both are simply called "an ounce" in conversation. A jeweller quoting ounces almost certainly means troy ounces. A courier quoting ounces certainly does not. Because the two differ by roughly a tenth, the ambiguity is expensive rather than academic, which is why converting from grams is the safer habit: a gram is a gram in every trade.
What the mistake actually costs
Take a 100 gram bar and convert it both ways:
ordinary 100 ÷ 28.349523125 = 3.5274 oz
error (3.5274 − 3.2151) ÷ 3.2151 = 9.71%
Quoting 3.5274 ounces to a buyer who pays per troy ounce claims about a tenth more metal than is present. On a single 100 gram bar that is roughly a third of a troy ounce of gold being claimed in error. The mistake runs in both directions: a seller using the wrong ounce undercharges, a buyer using it overpays, and neither notices until the metal is weighed again.
The troy pound is not the pound you know
A troy pound is 373.2417216 grams, not the 453.59237 grams of an ordinary pound. It contains twelve troy ounces rather than sixteen ounces, which is why it is lighter despite the troy ounce being heavier. The troy pound is effectively obsolete in trade and is worth knowing about mainly so that it is not assumed when someone says "pound" about metal.
In practice, bullion is quoted per troy ounce or per kilogram, and scrap is weighed in grams. Pounds rarely appear at all. If a figure in pounds does appear, it is worth confirming which pound is meant before agreeing a price.
Grams to troy ounces
This table converts common gold weights. The troy column uses 31.1034768 grams per troy ounce and the ordinary column uses 28.349523125 grams per ounce, both exact.
| Grams (g) | Troy ounces | Ordinary ounces | Pounds (lb) |
|---|---|---|---|
| 1 g | 0.0322 oz t | 0.0353 oz | 0.0022 lb |
| 5 g | 0.1608 oz t | 0.1764 oz | 0.0110 lb |
| 10 g | 0.3215 oz t | 0.3527 oz | 0.0220 lb |
| 20 g | 0.6430 oz t | 0.7055 oz | 0.0441 lb |
| 31.1035 g | 1.0000 oz t | 1.0971 oz | 0.0686 lb |
| 50 g | 1.6075 oz t | 1.7637 oz | 0.1102 lb |
| 100 g | 3.2151 oz t | 3.5274 oz | 0.2205 lb |
| 250 g | 8.0377 oz t | 8.8185 oz | 0.5512 lb |
| 500 g | 16.0754 oz t | 17.6370 oz | 1.1023 lb |
| 1000 g | 32.1507 oz t | 35.2740 oz | 2.2046 lb |
The 31.1035 g row is worth noting: that weight is exactly one troy ounce, and it is the standard size for a small gold bar or coin. Note that it is 1.0971 ordinary ounces, not one.
Buying and selling scrap
Scrap gold is almost always weighed in grams, and this is deliberate. A gram is unambiguous, whereas an ounce needs qualifying. When a price is quoted per gram, multiply directly. When it is quoted per troy ounce, divide the grams by 31.1034768 first.
Purity is a separate calculation from weight and the two are often confused. A 10 gram item of 18 carat gold contains 18/24 of its weight in gold, which is 7.5 grams of pure gold, or 0.2411 troy ounces. Converting the unit does not tell you the purity, and a scrap price applies to the pure content rather than to the total weight.
The exact constants used throughout this site, including the troy ounce, are published on the methodology page. Nothing here is financial advice; confirm any transaction against a calibrated, certified scale.