Troy Ounce vs. Ounce: What’s the Difference?

One troy ounce weighs 31.1034768 grams, while one regular—or avoirdupois—ounce weighs 28.349523125 grams. A troy ounce is therefore about 9.7% heavier than a regular ounce. Gold, silver, platinum, and palladium prices are normally quoted per troy ounce, so using the wrong ounce can produce an incorrect metal value and premium.

Here is the difference at a glance:

Calculate fine metal weight and bullion premium →

Is a Troy Ounce the Same as a Regular Ounce?

No. They are two different units of mass that happen to use the same word: ounce.

The troy ounce belongs to the troy weight system traditionally used for precious metals. The regular ounce belongs to the avoirdupois system used for most other goods measured in ounces or pounds.

The National Institute of Standards and Technology gives the precise precious-metals conversion:

1 troy ounce = 31.1034768 grams

NIST lists the regular avoirdupois ounce separately at approximately 28.34952 grams in its Guide to the SI conversion factors.

The relationship between the two units is:

1 troy ounce ≈ 1.09714286 regular ounces

1 regular ounce ≈ 0.91145833 troy ounce

This difference is large enough to matter. If a product actually weighs one regular ounce but is mistakenly treated as one troy ounce, its precious-metal weight will be overstated by about 9.7%.

Why Are Precious Metals Measured in Troy Ounces?

The troy system remains the standard convention for quoting and trading precious metals. Gold, silver, platinum, and palladium spot prices are commonly expressed as a price per troy ounce, and many bullion coins, rounds, and bars state their metal content in troy ounces.

Using one standard unit allows products from different mints, refiners, dealers, and countries to be compared on the same basis. A price of $2,400 per troy ounce of gold and a coin containing 0.25 troy ounce of fine gold can be combined directly:

0.25 troy oz × $2,400 per troy oz = $600 metal value

The same calculation would be wrong if the product’s weight were actually 0.25 regular ounce. Units must match before weight is multiplied by spot price.

The Royal Mint also defines a troy ounce as 31.1034768 grams and notes that the troy system uses 12 ounces to a pound rather than the 16 ounces used in the regular avoirdupois system.

How Many Grams Are in a Troy Ounce?

There are exactly 31.1034768 grams in one troy ounce for precious-metals conversions.

Common troy-ounce weights are:

To convert troy ounces to grams:

Grams = Troy ounces × 31.1034768

For example, a five-troy-ounce silver bar has a nominal weight of:

5 × 31.1034768 = 155.517384 grams

Product specifications and household scales may display fewer decimal places. Rounding the final result is normally appropriate, but keeping the full conversion factor during the calculation prevents avoidable errors.

How to Convert Grams to Troy Ounces

To convert grams to troy ounces:

Troy ounces = Grams ÷ 31.1034768

For example, 100 grams equals:

100 ÷ 31.1034768 = 3.21507466 troy ounces

One kilogram contains:

1,000 ÷ 31.1034768 = 32.1507466 troy ounces

Useful gram conversions include:

These figures convert total mass only. If a coin or bar is not pure metal, purity must still be considered before calculating fine metal content or melt value.

Troy Ounce Symbols and Product Labels

You may see a troy ounce written in several ways:

• troy ounce;
• troy oz;
• oz t;
• oz T;
• ozt.

NIST uses oz T in its precious-metals conversion table. Dealers, mints, refiners, auction listings, and scale manufacturers may use other abbreviations.

An inscription such as 1 oz fine silver on a recognized bullion product usually refers to one troy ounce of fine silver, not one ordinary household ounce. However, the safest approach is to read the manufacturer’s or mint’s complete specification rather than relying on an isolated “oz” label.

Check whether a specification describes:

• total product weight;
• fine precious-metal content;
• both gross weight and fine content;
• a minimum guaranteed metal content.

These descriptions are related but are not interchangeable.

Gross Weight vs. Fine Metal Weight

The difference between ounce systems is only one part of the calculation. You must also distinguish the product’s gross weight from its fine metal weight.

• Gross weight is the total weight of the product, including precious metal and any alloy metals.
• Fine metal weight is the weight of the selected pure precious metal contained in the product.

If the product specification gives only gross weight and purity:

Fine metal weight = Gross weight × Purity

If the weight is in grams:

Fine metal content in troy ounces = Gross weight in grams × Purity ÷ 31.1034768

For example, a hypothetical 26.73-gram coin made from .900 fine silver contains:

26.73 g × 0.900 = 24.057 g of fine silver

Converted to troy ounces:

24.057 ÷ 31.1034768 = 0.77345 troy oz of fine silver

Its gross weight is 26.73 grams, but its silver content is approximately 24.057 grams, or 0.77345 fine troy ounce.

When a “One-Ounce” Coin Weighs More Than One Troy Ounce

Some bullion coins contain one full troy ounce of fine precious metal but weigh more than one troy ounce overall because they also contain alloy metals.

The one-ounce American Gold Eagle is a useful example. According to the United States Mint’s bullion coin specifications, it is 91.67% gold, with silver and copper added for durability. Its gross weight is 1.0909 troy ounces, or 33.931 grams, but it contains the stated 1 troy ounce of pure gold.

For this product:

• gross coin weight: 1.0909 troy oz;
• fine gold content: 1.0000 troy oz;
• the remaining weight: alloy metals.

If you are calculating its gold value, use the official fine gold content of one troy ounce. Do not multiply that stated fine content by 91.67% again. Doing so would apply purity twice and understate the gold value.

The same principle applies to any product whose official specification already states its fine metal content. Use the declared fine content directly unless you have a specific reason to verify it from more detailed measurements.

Example 1: A 100-Gram .9999 Gold Bar

Consider a hypothetical gold bar with:

• gross weight: 100 grams;
• purity: .9999;
• gold spot price: $2,400 per troy ounce.

First calculate its fine gold weight in grams:

100 g × 0.9999 = 99.99 g of fine gold

Convert the fine gold weight to troy ounces:

99.99 ÷ 31.1034768 = 3.214753 troy oz

Calculate its metal value:

3.214753 × $2,400 = $7,715.41

If the manufacturer instead guarantees that the bar contains 100 grams of fine gold, use that guaranteed fine content directly. Product wording matters: “100 g total weight at .9999 purity” and “100 g fine gold” are not necessarily identical specifications.

Example 2: A 90% Silver Coin in Grams

Suppose a hypothetical silver coin has:

• gross weight: 26.73 grams;
• purity: .900;
• silver spot price: $32 per troy ounce.

Its fine silver weight is:

26.73 × 0.900 = 24.057 grams

Convert that figure to troy ounces:

24.057 ÷ 31.1034768 = 0.77345 troy oz

Its calculated silver value is:

0.77345 × $32 = $24.75

Multiplying the gross gram weight by a price per troy ounce would mix incompatible units. Treating the coin as 26.73 troy ounces would produce an even larger error.

Example 3: What Happens If You Use a Regular Ounce?

Assume an item contains exactly one regular avoirdupois ounce—28.349523125 grams—of pure silver. Silver spot is $32 per troy ounce.

The item’s actual weight in troy ounces is:

28.349523125 ÷ 31.1034768 = 0.91145833 troy oz

Its metal value is therefore:

0.91145833 × $32 = $29.17

If it were incorrectly treated as one full troy ounce, the calculated value would be $32. The mistake would overstate the metal value by about $2.83, or 9.7% relative to the correct value.

The same unit error would also affect the calculated bullion premium. An overstated melt value makes the premium appear lower than it really is.

How to Convert Spot Price per Troy Ounce to Price per Gram

Dealer pages and market charts frequently show spot price per troy ounce, while smaller bars and coins may be labeled in grams.

To calculate the spot price per gram:

Price per gram = Price per troy ounce ÷ 31.1034768

At a hypothetical gold spot price of $2,400 per troy ounce:

$2,400 ÷ 31.1034768 = $77.16 per gram

To convert a price per gram back to a price per troy ounce:

Price per troy ounce = Price per gram × 31.1034768

These formulas are useful when comparing a gram-denominated product with a market price quoted per troy ounce. Make sure the price and product use the same currency and refer to the same metal.

How to Use Purity With Troy-Ounce Calculations

Purity indicates how much of a product’s gross weight is the selected precious metal. It may be displayed as a decimal, percentage, fineness, or karat value.

The Royal Mint’s guide to metal fineness explains that fineness expresses precious-metal content in parts per thousand. For example, .9999 gold represents 99.99% gold.

Use the official product specification whenever one is available. Rounded purity values can create small differences, particularly when they are combined with rounded weights.

Can You Use a Kitchen Scale for Bullion?

A digital scale that measures grams can help perform a basic weight check, provided that it has sufficient resolution and has been calibrated correctly. Grams avoid the ambiguity between troy and regular ounces.

Many household scales show oz as regular avoirdupois ounces. Do not assume that an ounce mode is a troy-ounce mode unless the scale documentation explicitly says so. Some jewelry scales include a separate ozt mode, while others offer only grams, regular ounces, carats, or grains.

For a simple check:

1. Select grams.
2. Confirm the scale reads zero with the empty platform.
3. Weigh the product without packaging or a capsule unless the official specification includes it.
4. Compare the result with the mint or refiner’s stated gross weight.
5. Use purity or stated fine content separately when calculating metal value.

A household scale cannot establish authenticity or exact purity. Packaging, capsules, wear, scale accuracy, and manufacturing tolerances can all affect the displayed weight.

Common Troy-Ounce Mistakes

Assuming every “oz” means troy ounce

Precious-metal products and spot prices usually use troy ounces, but ordinary scales and shipping weights commonly use regular ounces. Check the context and product specification.

Using 28.35 grams for a bullion ounce

Approximately 28.35 grams is one regular avoirdupois ounce. One troy ounce is 31.1034768 grams.

Confusing gross weight with fine metal content

An alloyed coin can weigh more than its stated fine gold or silver content. Calculate value using the selected precious metal, not the total weight of all metals.

Applying purity twice

If a specification already states “1 oz fine gold,” that figure normally describes the fine gold content. Do not multiply it by purity again.

Ignoring purity when only gross weight is supplied

If the specification gives total weight and fineness but not fine content, multiply the gross weight by purity before calculating melt value.

Multiplying grams directly by spot price per troy ounce

Convert grams to troy ounces, or convert the spot price to a price per gram. The weight unit and price unit must match.

Rounding too early

Using 31.1 grams instead of 31.1034768 may be adequate for a quick estimate, but repeated early rounding can create noticeable differences for large bars or high-priced metals. Keep additional decimal places until the final result.

Including packaging in the metal weight

A capsule, assay card, sleeve, or presentation box is not precious-metal content. Use the manufacturer’s specification rather than weighing a packaged product as one unit.

Confusing weight ounces with fluid ounces

A fluid ounce measures volume. A troy ounce and an avoirdupois ounce measure mass. Fluid-ounce conversions do not belong in bullion calculations.

Frequently Asked Questions

Is a troy ounce heavier than a regular ounce?

Yes. A troy ounce weighs 31.1034768 grams, while a regular ounce weighs 28.349523125 grams. The troy ounce is approximately 9.714% heavier.

How many grams are in one troy ounce of gold?

One troy ounce is 31.1034768 grams regardless of the metal. If a product contains exactly one fine troy ounce of gold, its fine gold content is 31.1034768 grams.

How many grams are in one troy ounce of silver?

One fine troy ounce of silver is also 31.1034768 grams. The unit does not change between gold, silver, platinum, or palladium.

How many troy ounces are in one kilogram?

One kilogram equals approximately 32.1507466 troy ounces.

Is oz on a digital scale a troy ounce?

Usually not. On many household scales, oz means regular avoirdupois ounces. Look for a separate ozt, oz t, or troy-ounce mode in the scale documentation, or use grams.

Does a one-ounce gold coin always weigh 31.1034768 grams?

No. It may contain one troy ounce of fine gold while weighing more overall because of alloy metals. The one-ounce American Gold Eagle, for example, contains one fine troy ounce of gold but has a gross weight of 33.931 grams.

Why is a troy pound lighter if a troy ounce is heavier?

A troy pound contains 12 troy ounces, while a regular avoirdupois pound contains 16 regular ounces. The individual troy ounce is heavier, but the troy pound contains fewer ounces.

Is a 1 oz silver bar 31.1 grams?

A bar specified as one troy ounce has a nominal troy weight of 31.1034768 grams. Read the product specification to determine whether the label refers to gross weight or guaranteed fine silver content and to see how the manufacturer states tolerances.

Should I use troy ounces or grams in a bullion calculator?

Either unit works if it is entered correctly. Use the unit shown in the official product specification, then confirm whether the value represents gross weight or fine metal content. Avoid converting back and forth unnecessarily.

Match the Weight Unit Before Calculating Value

A troy ounce and a regular ounce are not interchangeable. For precious metals, the critical conversion is:

1 troy ounce = 31.1034768 grams

Before calculating melt value or premium, identify the product’s weight unit, determine whether the stated weight is gross or fine, and apply purity only when necessary. Once fine metal content and spot price use the same unit, the remaining calculation is straightforward.

The web calculator accepts troy-ounce weight and calculates fine metal content, melt value, and premium. The iPhone app also supports gram-based calculations and saved comparisons.

All prices and examples in this article are hypothetical and use fixed values for illustration. This material is provided for general informational purposes only and does not constitute financial, investment, tax, legal, appraisal, authentication, or refining advice.