Troy Ounce vs Ounce: What's the Difference and Why Gold Uses Troy

Short answer: a troy ounce is 31.1035 grams, while the regular ounce you use for food, the avoirdupois ounce, is 28.3495 grams. The troy ounce is about 9.7% heavier. Gold, silver, platinum and palladium are priced and traded in troy ounces, so when a news site says gold costs a certain amount "per ounce", it means a troy ounce.

• 1 troy ounce = 31.1035 g = 1.0971 avoirdupois ounces.
• 1 avoirdupois ounce = 28.3495 g = 0.9115 troy ounces.
• 1 pound (16 oz) = 453.592 g = 14.583 troy ounces.
• Spot prices are always per troy ounce.

The two ounces side by side

	Troy ounce	Avoirdupois ounce
Grams	31.1035	28.3495
Used for	Gold, silver, platinum, palladium	Food, mail, most everyday goods
Ounces in a pound	12 (troy pound)	16
Pound in grams	373.24	453.59

The two systems use the same word, but their pounds are different too. The troy pound has 12 ounces, while the everyday pound has 16. See the glossary entries for troy ounce and avoirdupois ounce.

Why precious metals use troy weight

Troy weight has been used in Europe since the Middle Ages, when it was the standard for weighing coins and precious metals. When modern metals markets formed, they adopted the unit, and it has stayed. Today every major bullion price, bar and coin is quoted per troy ounce, and each ounce of metal sold is a troy ounce no matter where in the world you buy it.

How to convert

To convert	Multiply by
Troy ounces to grams	31.1035
Grams to troy ounces	0.03215
Troy ounces to avoirdupois ounces	1.09714
Avoirdupois ounces to troy ounces	0.91146
Pounds to troy ounces	14.5833
Kilograms to troy ounces	32.1507

The gram to troy ounce converter and the bullion weight tables do the arithmetic for you.

Worked examples

• Price per gram. If gold is $4,000 per troy ounce (an illustrative figure), a gram of pure gold is $4,000 ÷ 31.1035 = about $128.60.
• A pound of silver. A pound of silver is 14.583 troy ounces. At $50 per troy ounce, that is about $729. Treating those 16 ounces as troy ounces would give $800, an overstatement of about 9.7%.
• A kilo bar. One kilogram is 32.1507 troy ounces, so a kilo of gold at $4,000 per ounce is about $128,600.

Mistakes to avoid

• Using kitchen weights for metal. If you weigh silver on a food scale set to ounces, you are reading avoirdupois ounces, not troy ounces.
• Mixing up the pounds. A troy pound has 12 ounces and a normal pound has 16.
• Assuming a coin's total weight equals the metal weight. Some coins, such as the American Gold Eagle, weigh slightly more than a troy ounce because of the alloy, while containing exactly one troy ounce of gold.
• Comparing prices across units. A price per gram and a price per troy ounce need converting before they can be compared.

See the guide to weighing gold and silver accurately for scale tips.

Weights you will see on coins and bars

Product	Typical weight
1 oz silver coin	1 troy oz of silver (31.1035 g)
10 oz silver bar	10 troy oz (311.035 g)
100 oz silver bar	100 troy oz (about 3.11 kg)
Kilo gold bar	1 kg (32.1507 troy oz)
400 oz gold bar	400 troy oz (about 12.44 kg)

Track weight in the unit you prefer

BullionKeeper stores weights in grams and shows them in troy ounces, grams or kilograms, so you can match the unit used by your dealer or the spot price without redoing the sums.