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What Is a Troy Ounce? (And Why Gold Is Priced in It)
Every gold and silver spot price you'll ever see — on a dealer's board, on the news, in the app — is quoted per troy ounce: 31.1035 grams, about 10% heavier than the ounce your kitchen scale measures. Here's exactly how the unit converts, where it comes from, and how to turn a per-troy-ounce spot price into the per-gram and per-pennyweight prices used at the counter.
How much does a troy ounce weigh?
One troy ounce (written ozt) weighs 31.1035 grams — 31.1034768 g to be precise — which is about 9.7% more than the avoirdupois ounce (28.35 g) that kitchen and postal scales measure. It divides cleanly into the other units of the troy system:
| Unit | One troy ounce equals |
|---|---|
| Grams | 31.1035 g |
| Pennyweight | 20 dwt |
| Grains | 480 gr |
| Regular (avoirdupois) ounces | 1.0971 oz |
| Kilograms | 0.0311 kg |
Going the other way: 1 gram = 0.03215 ozt and 1 kilogram = 32.1507 ozt. Those constants are fixed — they never move with the market.
Why is gold priced in troy ounces?
Tradition and standardization. The troy system is traditionally traced to the medieval trade fairs of Troyes, France, where merchants from across Europe needed one agreed weight for settling precious-metal trades. England made it the legal standard for gold and silver in 1527, and the US Mint adopted the troy pound for coinage in 1828. When the rest of daily life moved on to metric, the bullion market simply never switched.
That stubbornness is a feature: the London and New York markets both quote dollars per troy ounce, so a spot price means exactly the same weight of metal everywhere. One unit, no ambiguity, centuries of contracts behind it.
Troy ounce vs regular ounce: what's the difference?
A troy ounce is 31.1035 g; the regular (avoirdupois) ounce is 28.35 g — so the troy ounce is about 9.7% heavier. Both descend from the old grain unit: a troy ounce is 480 grains, while an avoirdupois ounce is 437.5 grains.
The pounds flip the other way, which trips people up: a troy pound is only 12 troy ounces (373.24 g), while the everyday pound is 453.59 g. So the troy ounce is heavier than a regular ounce, but the troy pound is lighter than a regular pound.
The mix-up that costs real money is the kitchen scale. Weigh out one "ounce" of gold on a kitchen scale and you have 28.35 g — only 0.911 troy ounces. Price that against a spot of, say, $4,000 per troy ounce (a round example, not today's price) and it's worth about $3,646, not $4,000. Call the units wrong on a bigger lot and the error scales with it.
How do you turn a spot price into a per-gram or per-dwt price?
Divide the spot price by 31.1035 for a per-gram price, or by 20 for a per-pennyweight price. Sticking with the $4,000 example spot: pure gold runs $4,000 ÷ 31.1035 = $128.60 per gram, or $4,000 ÷ 20 = $200 per dwt. Then multiply by purity — 14K is 58.3% gold, so 14K scrap is worth about $75.01 per gram, and a 6-gram 14K ring melts at roughly $450. The full formula is worked through step by step in how to calculate scrap gold value, and the pennyweight side has its own guide.
Silver works identically. If silver were $50 per troy ounce, pure silver would be $50 ÷ 31.1035 = $1.61 per gram, and sterling (92.5%) about $1.49 per gram. Junk-silver buyers lean on the same unit: $1 of face value in 90% US coins contains about 0.715 troy ounces of silver.
Frequently asked questions
How many grams are in a troy ounce?
One troy ounce equals 31.1035 grams. That makes it about 10% heavier than the regular (avoirdupois) ounce of 28.35 grams, and it splits evenly into 20 pennyweight (dwt) or 480 grains.
Why is gold priced in troy ounces?
Tradition and standardization. The troy system is traditionally traced to the medieval trade fairs of Troyes, France, and became England's legal standard for gold and silver in 1527. Bullion markets worldwide kept it, so a spot quote in London and New York means exactly the same weight.
What does ozt mean?
ozt is the abbreviation for troy ounce — you will also see t oz or toz. Most jewelers' scales offer it as a weighing mode alongside grams and pennyweight, so always confirm which mode the display is showing before you price anything.
Is a pound of gold 16 ounces?
No. Precious metals use the troy pound, which is 12 troy ounces, about 373.24 grams. An everyday 16-ounce avoirdupois pound is 453.59 grams — about 14.58 troy ounces. Oddly, the troy ounce is heavier than the regular ounce, but the troy pound is lighter than the regular pound.
Estimate it in seconds
You never have to do the 31.1035 division by hand. Scrap Gold Pro takes the live per-troy-ounce spot price and reprices every karat and purity in grams, pennyweight, troy ounces, or kilograms — switch the unit and every number updates instantly. It's free on web, iOS, and Android.