How to Calculate the Pure-Gold Content of Jewellery

A gold necklace can weigh 30 grams without containing 30 grams of pure gold. Most jewellery is made from an alloy, meaning gold is mixed with other metals to improve strength, colour or workability. To estimate the amount of pure gold in a piece, you need two things: its weight and its purity.

The calculation is straightforward once the purity is known. It can help you understand the metal content of your jewellery and estimate its theoretical gold value before dealer margins, making charges, stones, taxes or resale deductions are considered.

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The basic formula

If the jewellery is marked in karats, divide the karat by 24 and multiply by the item’s gold-alloy weight:

Pure gold content (g) = Jewellery weight (g) × Karat ÷ 24

If the item is marked by fineness, divide the fineness by 1,000:

Pure gold content (g) = Jewellery weight (g) × Fineness ÷ 1,000

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Example: 22K jewellery

Suppose a 22K bracelet weighs 40 grams.

40 × 22 ÷ 24 = 36.67 grams of pure gold

The bracelet therefore contains approximately 36.67 grams of gold, while the remaining 3.33 grams are other metals in the alloy. A 916 fineness calculation gives a very similar result: 40 × 0.916 = 36.64 grams.

Example: 18K jewellery

An 18K ring weighing 12 grams contains 75% gold because 18 ÷ 24 = 0.75.

12 × 18 ÷ 24 = 9 grams of pure gold

The other 3 grams are alloying metals. The same calculation can be made from a 750 fineness mark: 12 × 750 ÷ 1,000 = 9 grams.

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Quick purity reference

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Do not include stones in the gold weight

This is one of the most important practical limitations. A jewellery item may contain diamonds, gemstones, enamel, non-gold fittings or other materials. If the total weight includes those components, multiplying the full weight by the purity will overstate the amount of gold.

For a more accurate calculation, use the net metal weight if it is available on the invoice, valuation certificate or dealer record. If the stone weight is known in carats, remember that gemstone carats are a unit of mass and are not the same as gold karats, which describe purity.

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Be careful with hollow jewellery

Hollow jewellery can look large while containing less metal than a solid piece of similar dimensions. The formula still works, but only if the actual measured weight is used. Appearance is not a reliable guide to gold content.

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What if the item is stamped 916, 875, or 750?

These are fineness marks. They show the proportion of gold in parts per thousand. A 916 item is approximately 91.6% gold, 875 is 87.5%, and 750 is 75%.

The World Gold Council describes fineness as precious-metal content expressed in parts per thousand. This is why a 750 mark corresponds to 18K gold, while 916 corresponds closely to 22K.

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How to estimate the metal value after finding the pure-gold content

Once you know the approximate grams of pure gold, you can multiply that figure by the current 24K reference price per gram to estimate the theoretical value of the gold content.

Estimated underlying gold value = Pure gold content (g) × Current 24K price per gram

For example, imagine a 22K bracelet contains 36.67 grams of pure gold and the 24K reference rate is US$140 per gram. The theoretical metal value would be approximately US$5,133.80. This is only an illustrative example, not a current market quote.

A dealer’s actual buyback offer may be lower because of testing, refining, operational costs, margins, and local market conditions. A retail purchase price may be higher because of craftsmanship, branding, making charges, stones, taxes, or dealer premiums.

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Why not simply multiply the jewellery weight by the 22K or 18K rate?

You can. If you already have a reliable live price per gram for the exact purity, multiplying the net gold-alloy weight by that purity-specific rate is a convenient way to estimate the underlying gold value.

Calculating pure-gold content separately is still useful because it shows exactly how much fine gold the item contains. It also lets you compare pieces of different purities on the same 24K basis.

GoldRates publishes separate reference prices for common purities at GoldRates.com, which can make this comparison easier.

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What if you do not know the purity?

Do not assume purity from colour alone. Yellow, white and rose gold can all be manufactured at different karat levels. Look for a recognised karat or fineness mark and, for valuable items, consider professional testing if the mark is absent, unclear or doubtful.

Hallmarking rules vary by country. In formal hallmarking systems, independent testing can provide stronger assurance than an unverified stamp. Buyers should check the local requirements applicable to the item and market.

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A practical checklist

• Weigh the jewellery accurately in grams.
• Identify the karat or fineness mark.
• Exclude stones and non-gold components from the metal weight where possible.
• Convert the purity to a fraction, such as 22/24 or 916/1,000.
• Multiply the net metal weight by that purity fraction.
• Use the current 24K reference price if you want to estimate the underlying pure-gold value.
• Treat any retail or buyback quote separately from the theoretical metal value.

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The key takeaway

To calculate the pure-gold content of jewellery, multiply its net gold-alloy weight by its purity. A 22K item is roughly 91.6% gold, a 21K item is 87.5%, and an 18K item is 75%. The calculation gives you the approximate amount of fine gold contained in the piece.

That figure is useful for understanding metal value, but it is not the same as a retail price or guaranteed resale offer. Jewellery can carry additional value or costs from design, stones, labour, brand, taxes, and dealer margins, while resale offers can include deductions and spreads.