Troy Ounce Conversion Calculator
Troy against ordinary ounces, grams and grains.
Convert between troy ounces, grams, avoirdupois ounces, pennyweights and grains, the weights used for precious metals.
In grams
31.103 g
1.0000 troy oz · 20.00 dwt
A troy ounce is 31.1035 g against the ordinary ounce's 28.3495 — about 9.7% heavier. Confusingly, a troy pound is lighter than an ordinary pound, because it is twelve troy ounces rather than sixteen.
How the Troy Ounce Conversion Calculator works
A troy ounce is heavier than the ounce used for everything else — 31.10 grams against 28.35 — which means precious metals are weighed on a scale that overlaps confusingly with the kitchen one. The difference is nearly ten percent, and it runs in the direction that flatters a seller who gets it wrong.
Also known as: troy weight converter · troy ounce to gram calculator
Two ounce systems, one confusing overlap
A troy ounce is 31.1034768 grams; the avoirdupois ounce used for everything else is 28.349523125. The troy ounce is about 9.7% heavier, and both are called an ounce.
It gets worse with pounds. A troy pound is twelve troy ounces, 373.24 grams, while an avoirdupois pound is sixteen ordinary ounces, 453.59 grams. So the troy ounce is heavier and the troy pound is lighter — a genuinely counterintuitive pair.
Troy weight survives for precious metals because the whole trade standardised on it centuries ago. Gold, silver, platinum and palladium are all quoted per troy ounce; nothing else in a jeweller's shop is.
A worked example
A one ounce gold coin contains one troy ounce, 31.10 grams. Weighed on a kitchen scale set to ounces it reads 1.097 — nearly a tenth more than the label, because the scale is using avoirdupois.
The same confusion runs the other way in scrap. Selling 100 grams of gold and being quoted per ounce means asking which ounce: at $2,400 per troy ounce that is $7,716, and at $2,400 per avoirdupois ounce it would be $8,466. Nobody quotes the second, but the arithmetic matters when converting.
Where the answer misleads
The conversion itself is exact, so any error is in which unit was meant rather than in the maths. Where a quote is ambiguous, converting to grams removes the problem entirely — grams mean one thing everywhere.
Grains are a further trap. There are 480 grains to a troy ounce and 437.5 to an avoirdupois ounce, but the grain itself is the same in both systems. Old pearl and gemstone weights are sometimes given in grains, where four grains is almost exactly one metric carat.
Finally, bullion is sold in troy ounces but often described in grams for smaller bars, and the two are not interchangeable in the mind. A 20 gram bar is 0.643 troy ounces, not two thirds of anything convenient.
Frequently asked questions
How many grams in a troy ounce?
31.1034768 grams exactly. The ordinary avoirdupois ounce is 28.349523125 grams, so a troy ounce is about 9.7% heavier.
Why do precious metals use troy weight?
It descends from the medieval Troyes fair system and survived for bullion because the whole trade standardised on it. Gold, silver, platinum and palladium are all quoted per troy ounce; everything else in the shop is weighed avoirdupois.
Is a troy pound heavier than a normal pound?
No, lighter — and this is where it gets genuinely confusing. A troy pound is twelve troy ounces, which is 373 g, while an avoirdupois pound is sixteen ordinary ounces at 454 g. The ounce is heavier and the pound is lighter.
What is a grain?
1/480 of a troy ounce, about 64.8 mg. It is still used for pearls, some gemstones and for gunpowder. Four grains make one carat almost exactly, which is why old pearl weights are sometimes quoted in grains.