The quick answer: a standard ounce is about 28.35 grams. But if you are weighing gold or silver, the answer is 31.1035 grams — because precious metals use a different ounce. Here is why.
The two ounces
Ounce type
Grams
Used for
Standard (avoirdupois)
28.3495 g
Food, mail, everyday goods
Troy
31.1035 g
Gold, silver, platinum, palladium
So a troy ounce is about 10% heavier than the ounce on your kitchen scale. That difference matters a lot when you are pricing metal: at $2,000 per troy ounce, that extra 2.75 grams is real money.
Where the troy ounce comes from
The troy system dates back to the medieval trade town of Troyes in France and became the standard for weighing precious metals. It survived precisely because consistency matters most where value is highest. When you read a live gold price or a silver price, it is always per troy ounce.
Handy gram conversions
1 standard ounce = 28.35 g
1 troy ounce = 31.1035 g
1 pound = 16 standard ounces = 453.592 g
1 kilogram = 32.15 troy ounces
For any other weight conversion, our unit converter has a dedicated weight category — including both ounce types where relevant.
Convert grams and ounces
Switch between grams, ounces, pounds and kilograms instantly.
A standard (avoirdupois) ounce is about 28.35 grams. A troy ounce, used for precious metals, is about 31.1035 grams.
How many grams are in a troy ounce of gold?
A troy ounce of gold is 31.1035 grams.
The two ounces, side by side
Both figures below are exact by international agreement, not measured approximations — which is why they have not changed since 1959 and will not change again.
Unit
Grams
Used for
Avoirdupois ounce
28.349523125
Food, post, body weight — everyday use
Troy ounce
31.1034768
Gold, silver, platinum, palladium
Apothecaries’ ounce
31.1034768
Historic pharmacy; same as troy
US fluid ounce
29.5735 ml (volume)
Liquids — not a weight at all
Imperial fluid ounce
28.4131 ml (volume)
UK liquids; differs from the US measure
The troy ounce is about 9.7% heavier than the everyday ounce. On a single ounce of gold that gap is roughly 2.75 grams — at typical prices, a couple of hundred dollars. It is the most expensive rounding error in common circulation.
Why precious metals kept their own ounce
The troy system takes its name from Troyes, a major medieval trade fair town in France, and it survived because bullion markets had no reason to change. Its internal divisions differ too: a troy pound is 12 troy ounces (373.24 g), while an avoirdupois pound is 16 ounces (453.59 g). So a troy pound is lighter than a normal pound even though a troy ounce is heavier — a trap for anyone converting historical weights.
Quick conversions worth knowing
1 troy oz = 31.1035 g
1 oz (regular) = 28.3495 g
1 kg = 32.1507 troy oz
1 kg = 35.274 regular oz
1 tola (S. Asia) = 11.6638 g
1 tael (HK) = 37.4290 g
Reading a hallmark or a scale
Jewellery scales usually read in grams or pennyweight (dwt), not troy ounces. One pennyweight is 1/20 of a troy ounce, or 1.5552 g — if a buyer quotes “per dwt”, multiply by 20 to compare against a per-ounce spot price. And remember to apply purity: 18 ct is 0.750 fine, so 10 g of 18 ct contains 7.5 g of gold. Our unit converter handles the weights and the gold price page shows the current per-ounce benchmark.
Where the confusion causes real losses
Buying online. A “1 oz” bullion coin means one troy ounce. A “1 oz” silver-plated novelty may well mean the regular ounce.
Selling scrap. If the scale reads grams and the offer is per troy ounce, divide grams by 31.1035, never by 28.35.
Recipes and supplements. These always use the avoirdupois ounce; using 31.1 g would over-measure by nearly 10%.
Fluid ounces. A volume, and different in the US and UK. Never convert them to grams without knowing the substance’s density.
