Troy Ounce: Definition, Conversion Table, and History

A troy ounce is the unit of weight behind every gold and silver price you see. When a dealer lists a 1 oz American Gold Eagle or a news site reports the gold price, the “ounce” is a troy ounce, not the ounce on your kitchen scale. The difference is small per coin, but it adds up quickly once you buy more.

In this guide, we explain what a troy ounce is, how much it weighs in grams and regular ounces, and why the precious metals market still uses it. You will also find conversion tables, a short history, and today’s prices per troy ounce and per gram from our gold price chart.

What Is a Troy Ounce?

A troy ounce is a unit of mass from the troy weight system, used today almost only for precious metals. It is abbreviated as oz t, ozt, or t oz. In bullion listings, you will usually just see “oz”, because everyone in the trade knows which ounce is meant.

The modern definition is exact. According to the London Bullion Market Association (LBMA), 1 troy ounce equals 31.1034768 grams. The US National Institute of Standards and Technology (NIST) uses the same value in its precious metals conversion tables.

Think of it this way: a troy ounce and a regular ounce are like a US gallon and an imperial gallon. Same name, different size. You only need to know which one is in use.

Where you will see troy ounces

Troy ounces appear in almost every part of the precious metals market:

• Spot prices: the benchmark gold and silver prices are quoted in US dollars per troy ounce.
• Bullion coins: a “1 oz” Gold Eagle, Maple Leaf, or Silver Eagle contains one troy ounce of fine metal.
• Bullion bars: bars come in troy ounce sizes (1 oz, 10 oz, 100 oz) and in metric sizes (1 g to 1 kg).
• Futures and vaults: large trading contracts and vault holdings are counted in troy ounces.
• Jewelry and scrap: US jewelers and scrap buyers often use pennyweights, a smaller troy unit.

How Much Does a Troy Ounce Weigh?

How many grams are in a troy ounce? There are exactly 31.1034768 grams in one troy ounce, which most people round to 31.1 grams. Here is how it compares to other units:

• 1 troy ounce = 31.1034768 grams
• 1 troy ounce = 1.0971 avoirdupois (regular) ounces
• 1 troy ounce = 20 pennyweights (dwt)
• 1 troy ounce = 480 grains
• 1 kilogram = 32.1507 troy ounces
• 1 regular pound = 14.5833 troy ounces

The grain is the link between the two systems. Since the international yard and pound agreement of 1959, one grain is defined as exactly 64.79891 milligrams. A troy ounce has 480 grains, while a regular ounce has 437.5 grains. That is the whole difference in one line.

Troy ounce to grams: quick reference

Grams to troy ounces: common bar sizes

Many gold and silver bars are sold in metric sizes. How many troy ounces is a 100 gram bar? A 100 g bar holds 3.2151 troy ounces. The table below covers the usual sizes, which you can compare live on our gold bar price comparison.

See today’s prices for 100 g gold bars and 1 kg gold bars.

Troy Ounce vs Regular Ounce

The regular ounce is officially called the avoirdupois ounce (from Old French for “goods of weight”). It is the ounce used in the US for food, mail, and almost everything else. Here is the key difference:

• Troy ounce: 31.1034768 g, 480 grains, used for precious metals.
• Avoirdupois ounce: 28.349523125 g, 437.5 grains, used for everyday goods.

So which one is heavier? The troy ounce is heavier, by about 2.75 grams or 9.7%. Now for the twist that confuses many people.

The ounce is heavier, but the pound is lighter

A troy pound has only 12 troy ounces. A regular pound has 16 regular ounces. As a result, a troy pound weighs 373.24 grams, while a regular pound weighs 453.59 grams. In other words, a pound of feathers really is heavier than a pound of gold, if the gold is weighed in troy pounds.

Troy vs avoirdupois: full comparison

Why the Difference Matters When You Buy Gold

Does a 9.7% gap really matter? Yes, because at today’s prices every gram is worth a lot of money. On October 3, 2026, the spot price of gold was $4,141.80 per troy ounce. If you wrongly applied that price to a regular ounce, you would value one regular ounce of gold at $4,141.80, when it is really worth about $3,775.08. The error is $366.72 on a single ounce.

Here is a second example. Suppose a seller offers you “10 ounces of gold” and weighs it on a kitchen scale in regular ounces. You would receive about 283.5 grams instead of the 311.0 grams that 10 troy ounces contain. That is roughly 27.5 grams of gold missing, worth more than $3,600 at the October 3, 2026 spot price.

The fix is simple:

• check that the listing says troy ounces or grams, not just “ounces” on a household scale,
• compare prices per troy ounce or per gram, never per regular ounce,
• for scrap and jewelry, ask whether the buyer pays per gram or per pennyweight,
• use a melt value calculator such as our gold melt value tool.

Read also: Gold Purity, Fineness and Karat: What Is It and How to Check It

Precious Metal Prices per Troy Ounce and per Gram

Spot prices are always quoted per troy ounce. To get the price per gram, divide by 31.1034768. Here is what that looks like for all four precious metals:

Live versions of these numbers are on our pages for the gold price per gram, gold price per kilogram, silver price per gram, and platinum price per gram.

Troy Ounces in Coins and Bars

Bullion products are named after the fine metal they contain, not their total weight. This matters for 22 karat coins.

1 oz gold coins

A 1 oz American Gold Eagle is 22 karat gold, alloyed with silver and copper to make it harder. The coin weighs more than one troy ounce in total (about 33.93 grams), but it contains exactly one troy ounce of pure gold. The South African Krugerrand works the same way. Coins such as the Canadian Gold Maple Leaf and the American Gold Buffalo are .9999 fine, so their total weight is very close to 31.10 grams.

Compare dealer prices for the American Gold Eagle and other gold coins.

Fractional coins

Fractional gold coins are sold as 1/10, 1/4, and 1/2 troy ounce. A 1/10 oz coin contains 3.11 grams of gold. Smaller coins carry a higher premium per ounce, because minting costs are spread over less metal.

Old US silver coins

Pre-1965 US dimes, quarters, and half dollars are 90% silver. Their silver content is usually given in troy ounces: a silver dime holds about 0.0723 troy ounces of silver and a silver quarter about 0.1808 troy ounces. Read more in our guides on silver dimes and silver quarters, or check the silver melt value calculator.

History of the Troy Ounce

Nobody knows exactly where troy weight began. The most common explanation is that it is named after the weights used at the medieval fairs of Troyes, a market town in the Champagne region of France. Merchants from across Europe traded there and needed a common standard for valuable goods.

Some historians also see Roman roots. The Romans divided their pound (libra) into 12 parts called unciae, the word that gave us “ounce”. The troy pound kept that 12 ounce structure. However, the Roman ounce weighed only about 27 grams, so it was not the same unit as today’s troy ounce.

England: from the Tower pound to the troy pound

According to the LBMA, troy units have been used to weigh precious metals in England since the 12th century or earlier. For a long time, the Royal Mint used a different standard called the Tower pound. In 1527, during the reign of Henry VIII, the verdict of the Trial of the Pyx (the annual test of the coinage) moved the basis for gold and silver from the Tower pound to the troy pound of 12 troy ounces.

The United States adopts troy weight

The troy ounce used today is essentially the British imperial troy ounce. The United States adopted the troy pound as the official weight standard for its coinage by an act of Congress on May 19, 1828. That is why the US Mint still describes its gold and silver bullion coins in troy ounces.

Section 2 of the 1828 act named one specific weight, brought from London, as the reference for all US coinage:

“[…] the brass troy pound weight procured by the minister of the United States at London, in the year one thousand eight hundred and twenty-seven, for the use of the mint, and now in the custody of the director thereof, shall be the standard troy pound of the mint of the United States, conformably to which the coinage thereof shall be regulated.”

US Congress, Act of May 19, 1828 (An Act to continue the mint at the city of Philadelphia), Section 2, United States Statutes at Large, Volume 4, May 1828

A precise modern definition

For centuries, the size of the troy ounce depended on physical reference weights kept by governments. The international yard and pound agreement of 1959 fixed the grain at exactly 64.79891 milligrams. Since a troy ounce is 480 grains, its value became exactly 31.1034768 grams.

In the UK, the Weights and Measures Act 1985 left the troy ounce as the only troy unit allowed in trade, and only for precious metals. The troy pound is no longer used for trading anywhere.

Other Troy Units: Pennyweight, Grain, and Troy Pound

You do not need these units to buy bullion, but you will meet them in jewelry shops and old documents:

• Grain (gr): the smallest unit, 64.79891 mg. Originally based on the weight of a grain of cereal.
• Pennyweight (dwt): 24 grains, or 1.5552 grams. There are 20 pennyweights in a troy ounce. The “d” comes from the Roman denarius, the old symbol for a penny.
• Troy pound (lb t): 12 troy ounces, or 373.2417 grams. No longer used in trade.

Why do jewelers like pennyweights? Because rings and chains weigh only a few grams, and a pennyweight is a convenient size for small pieces. If a buyer quotes a price per pennyweight, multiply by 20 to get the price per troy ounce of that alloy.

How to Convert Troy Ounces: Simple Formulas

You can do every conversion with a few formulas:

• grams = troy ounces × 31.1035
• troy ounces = grams ÷ 31.1035
• regular ounces = troy ounces × 1.0971
• troy ounces = regular ounces × 0.9115
• price per gram = price per troy ounce ÷ 31.1035
• price per pennyweight = price per troy ounce ÷ 20

Example: what is a 50 g silver bar worth at spot? 50 ÷ 31.1035 = 1.6075 troy ounces. At $60.52 per troy ounce on October 3, 2026, that is about $97.29 of silver, before the dealer premium.

Common Mistakes With Troy Ounces

1. Weighing gold on a kitchen scale in ounces. A household scale shows regular ounces, which are 9.7% lighter.
2. Assuming a 1 oz coin weighs 31.1 grams. A 22 karat coin like the Gold Eagle weighs about 33.93 grams in total but contains one troy ounce of gold.
3. Comparing per-gram and per-ounce prices directly. Always convert to the same unit first.
4. Forgetting the premium. Spot price per troy ounce is the value of the metal. Coins and bars sell above it, and small items sell well above it.
5. Mixing up troy and regular pounds. A troy pound has 12 ounces, not 16.

Read also: What Are the Best Gold Coins to Buy?

Summary: Troy Ounce

Compare Prices per Troy Ounce Before You Buy

Now that you know what a troy ounce is, you can compare offers properly. The fair way to judge any coin or bar is its price per troy ounce of fine metal, compared with the spot price. The difference is the premium you pay.

metalsradar does that math for you. Compare 1 oz gold bars, browse investment gold from several dealers, or follow the silver price chart to see the price per troy ounce change during the day.

This article is for informational purposes only and is not investment or tax advice.