What is the difference between an avoirdupois ounce and a troy ounce?

An avoirdupois ounce weighs about 28.35 grams, while a troy ounce weighs about 31.10 grams. The troy ounce is approximately 9.7 percent heavier. Avoirdupois ounces measure everyday goods; troy ounces measure gold, silver, platinum, and palladium.

Why do precious metals use a different ounce?

The troy system predates the avoirdupois system and was established specifically for precious metals trading, originating from the French town of Troyes, a medieval trade fair center. When the avoirdupois system became standard for general commerce, precious metals retained the older troy system to maintain pricing consistency across centuries of trading records.

How do I convert avoirdupois ounces to troy ounces?

Multiply avoirdupois ounces by 0.9115 to get troy ounces. Alternatively, multiply by 28.3495 to convert to grams first, then divide by 31.1035 to get troy ounces. For rough mental math, subtract about 10 percent from the avoirdupois figure.

Ounces to Troy Ounces (oz to oz t) Converter

1 oz = 0.9115 oz t

1 Ounce equals 0.9115 Troy Ounces (1 oz = 0.9115 oz t). Convert Ounces to Troy Ounces with formula, table, and examples.

One avoirdupois ounce equals approximately 0.9115 troy ounces. Despite sharing the name 'ounce,' these two units differ by about 10 percent: an avoirdupois ounce is 28.3495 grams while a troy ounce is 31.1035 grams. The troy ounce is heavier and is used exclusively for precious metals, while the avoirdupois ounce measures everything else.

How to Convert Ounces to Troy Ounces

oz t = oz × 0.9114583333

Multiply the value in Ounces by 0.9114583333

Take your value in Ounces
Multiply by 0.9114583333
Read the result in Troy Ounces

Common Ounces to Troy Ounces Conversions

Ounces (oz)	Troy Ounces (oz t)	Status
1 oz	0.911458 oz t
2 oz	1.822917 oz t
5 oz	4.557292 oz t
10 oz	9.114583 oz t
25 oz	22.786458 oz t
50 oz	45.572917 oz t
100 oz	91.145833 oz t
500 oz	455.729167 oz t
1,000 oz	911.458333 oz t

Good to Know About Ounces to Troy Ounces Conversion

The troy ounce's name comes from Troyes, a city in the Champagne region of France that hosted major medieval trade fairs where merchants from across Europe converged. The weight standards used at these fairs became the basis for precious metals trading throughout Europe, and the troy system's survival into the 21st century makes it one of the longest-lived commercial standards in Western civilization.

Ounces to Troy Ounces: What You Need to Know

When gold prices are quoted at '$2,000 per ounce,' that is per troy ounce, not the common ounce used at the grocery store. A gold investor buying what they think is one ounce of gold receives 31.1 grams, not 28.35 grams. This distinction matters critically in precious metals trading, where the 2.75-gram difference per ounce adds up to significant value across large transactions.

What is a Ounce? oz

An imperial and US customary unit of mass equal to approximately 28.35 grams. Commonly used in the US and UK for food and postal weight.

Imperial Us-customary food packaging (US/UK) postal weight cooking (US)

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What is a Troy Ounce? oz t

A troy ounce is a unit of mass used for precious metals such as gold, silver, and platinum. It equals exactly 31.1034768 grams, about 10% heavier than the common avoirdupois ounce.

Troy gold trading silver pricing platinum markets

Learn more about Troy Ounce →

Going the other way? Use our Troy Ounces to Ounces converter.

Ounces to Troy Ounces FAQ

An avoirdupois ounce weighs about 28.35 grams, while a troy ounce weighs about 31.10 grams. The troy ounce is approximately 9.7 percent heavier. Avoirdupois ounces measure everyday goods; troy ounces measure gold, silver, platinum, and palladium.
The troy system predates the avoirdupois system and was established specifically for precious metals trading, originating from the French town of Troyes, a medieval trade fair center. When the avoirdupois system became standard for general commerce, precious metals retained the older troy system to maintain pricing consistency across centuries of trading records.
Multiply avoirdupois ounces by 0.9115 to get troy ounces. Alternatively, multiply by 28.3495 to convert to grams first, then divide by 31.1035 to get troy ounces. For rough mental math, subtract about 10 percent from the avoirdupois figure.

Non-Frequently Asked Questions About Ounces to Troy Ounces

Questions nobody should ask - but someone did.

No, you actually get more gold per 'ounce' than you would if gold were sold in avoirdupois ounces. The troy ounce gives you 31.1 grams versus 28.35 grams, so the troy system is slightly generous by avoirdupois standards. Of course, the price per troy ounce already reflects this, so no one is getting a secret deal.
In a manner of speaking. The avoirdupois ounce controls the general merchandise territory (food, packages, people), while the troy ounce holds exclusive rights to the precious metals district (gold, silver, platinum). They have coexisted in this uneasy arrangement since the Middle Ages without either managing to eliminate the other.
You would undercount your gold by about 9.7 percent. On a 10-ounce gold bar worth roughly $20,000 at current prices, that mistake would cost you about $1,940. This is why jewelers, refiners, and coin dealers are extremely particular about which ounce they mean, and why 'just an ounce' is never a safe assumption in the gold business.