What Is a Troy Ounce? How Much It Weighs and Why Metals Use It

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A troy ounce is the unit used to weigh and price precious metals, and it equals exactly 31.1034768 grams. A standard (avoirdupois) ounce, the one used for food and postage in the U.S., weighs about 28.35 grams. A troy ounce is therefore roughly 10% heavier (1 troy oz ≈ 1.097 standard oz). When a gold, silver, platinum or palladium price is quoted “per ounce,” the ounce is a troy ounce, often written “troy oz” or “ozt.”

Troy ounce vs. standard ounce

Both units are defined through the grain, a tiny unit shared by the troy and avoirdupois systems. Since the 1959 international yard and pound agreement, one grain has been fixed at exactly 64.79891 milligrams. That definition is why the troy ounce has a precise metric value instead of a rounded one.

The gap per ounce is about 2.75 grams. That barely matters for one coin, but it compounds with quantity. If someone weighed 100 troy ounces of silver on a kitchen scale set to standard ounces, the scale would read about 109.7 ounces. Treating the two ounces as interchangeable would understate or overstate value by roughly 10%.

The pounds work the other way round. A troy ounce is heavier than a standard ounce, but a troy pound holds only 12 of them, so it weighs about 0.823 standard pounds. A standard pound contains about 14.58 troy ounces (7,000 grains ÷ 480 grains).

Troy ounce conversion table

The reverse conversions people need most often:

• 1 kilogram = 32.1507 troy ounces
• 1 gram = 0.03215 troy ounces
• 1 standard pound = 14.583 troy ounces
• 1 standard ounce = 0.9115 troy ounces

Converting a metal price between units

Because metal prices are quoted per troy ounce, conversion means dividing or multiplying by the factors above. The examples below use a hypothetical gold price of $1,000 per troy ounce, not a current or historical market price.

Price per gram. Divide the per-ounce price by 31.1035. $1,000 ÷ 31.1035 = about $32.15 per gram.

Price per kilogram. Multiply the per-ounce price by 32.1507. $1,000 × 32.1507 = about $32,150.70 per kilogram.

Price per standard ounce. Divide by 1.0971. $1,000 ÷ 1.0971 = about $911.50 per avoirdupois ounce.

Copper and other base metals. Copper is not quoted per troy ounce. U.S. copper futures are priced per standard pound, and the London Metal Exchange quotes per metric tonne. To express a copper price per troy ounce, divide the per-pound price by 14.583. Assuming a hypothetical copper price of $4.00 per pound, the result is $4.00 ÷ 14.583 ≈ $0.274 per troy ounce. Dealers selling copper rounds marketed as “1 troy oz” usually price them well above this melt value, because minting and distribution costs dominate at such low metal values.

Fine troy ounces vs. gross weight

A coin or bar has two weights: its gross weight, which includes any alloy metals, and its fine weight, which counts only the pure precious metal. Precious metals markets price fine weight, so a fine troy ounce means one troy ounce of pure gold, silver or other metal, whatever else is mixed in.

Fine weight is calculated as:

Fine weight = gross weight × fineness

Fineness is expressed in parts per thousand (for example, .999 or .9167) or in karats for gold, where 24 karat is pure and 22 karat is 22/24, or 91.67%.

A well-known example is the one-ounce American Gold Eagle. It is struck in 22-karat gold, so it weighs about 33.93 grams in total but contains one troy ounce (31.10 grams) of gold. The extra weight is copper and silver alloy added for durability. A pure .9999 gold coin of the same gold content weighs very close to 31.10 grams. Both coins carry the same value in gold even though they weigh different amounts on a scale.

Large bars work the same way. Gold bars traded in the London wholesale market are typically around 400 troy ounces, and their value is based on the fine ounces stamped or assayed for each bar, not on a round nominal size.

Where the troy system came from

The troy system is generally believed to take its name from Troyes, a city in the Champagne region of France that hosted major trade fairs in the Middle Ages. Merchants from across Europe and Britain met there, and a common set of weights made it easier to settle trades in silver, gold and other valuable goods. In that system, 480 grains made one troy ounce, and 12 troy ounces made one troy pound.

Some historians trace the ounce back further, to Rome. The Roman libra (pound) was divided into 12 unciae, and the word uncia is the root of both “ounce” and “inch.” The idea that Troyes merchants adapted Roman weights is a theory rather than settled fact, but the 12-part pound is common to both systems.

England had its own earlier standards for metals and gradually brought them in line with continental practice. The general-purpose avoirdupois system (“goods of weight”) was used for most commodities. Troy weights as they are known today were in use in England by the 15th century, and in 1527 England abolished the older Tower pound and made the troy pound the standard for gold and silver coinage. The United States adopted the troy pound for its Mint in 1828, which tied American coinage to troy weight.

Metrication later replaced most traditional units across Europe and much of the world, yet the troy ounce survived in bullion trading. Centuries of contracts, coin specifications, bar standards and price records were built on it, and changing the unit would have added conversion risk to every one of them.

The troy pound and the pennyweight

The full troy system has more units than the ounce:

• Grain: 64.79891 mg, the base unit shared with avoirdupois.
• Pennyweight (dwt): 24 grains, or about 1.555 grams. Twenty pennyweights make one troy ounce. The name comes from the weight of an old English silver penny, and “dwt” combines d (from the Latin denarius) with “wt” for weight.
• Troy ounce: 480 grains, or 20 pennyweights.
• Troy pound: 12 troy ounces, 5,760 grains, or about 373.24 grams.

The troy pound has largely fallen out of use. Bullion is quoted in troy ounces, grams or kilograms, not troy pounds. The pennyweight still appears in jewelry work and scrap gold buying, especially in the U.S., where some buyers quote prices per dwt. When comparing a per-pennyweight offer to the spot price, divide the per-ounce spot price by 20 and adjust for the karat of the item.

Where troy ounces are used today

The troy ounce is the main surviving unit of the troy system. Its main uses:

• Spot prices for gold, silver, platinum and palladium are quoted in U.S. dollars per troy ounce.
• Futures contracts on U.S. exchanges are sized in troy ounces. The standard COMEX gold futures contract, for example, covers 100 troy ounces.
• Bullion coins and bars from government mints and private refiners are sold in troy-ounce sizes (1 oz, 1/2 oz, 1/4 oz, 1/10 oz, 10 oz, 100 oz) alongside gram and kilogram sizes.
• Jewelry and scrap valuation, where the troy ounce and pennyweight are both used.

As for whether gold prices “on the stock market” are quoted in troy ounces: the gold spot and futures prices shown on financial sites are per troy ounce. A gold exchange-traded fund that trades on a stock exchange is priced per share, not per ounce. Each share represents a fraction of an ounce that varies by fund and declines slowly as fees are deducted, so an ETF’s share price cannot be read as a gold price without knowing the fund’s ounces per share.

FAQs

The Bottom Line

Anyone buying bullion, selling scrap jewelry or comparing metal prices needs to know which ounce a quote uses. A troy ounce is about 10% heavier than a kitchen-scale ounce, and dealers price the fine metal content, so check fineness and fine weight before comparing coins or bars. For gold ETFs, the share price reflects the fund's ounces per share, so it cannot be read as a per-ounce gold price.