Gold purity calculator

Convert karat to fineness, and find the fine-metal content of an alloy.

Quick answer: Divide the karat by 24 to get the gold share: 18K is 75% gold (750 fineness), 14K is 58.3% (583) and 22K is 91.7% (917). Multiply that share by the metal weight to get fine grams.

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Scenario chart

Price scenario range

Scenarios change one input while holding the others constant. They are calculations, not observed market prices or forecasts.

Detailed calculation table

The table contains the same inputs used for your result. Values are rounded for display; CSV preserves more precision.

Detailed calculator inputs and results
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From hallmark to fine-metal content

How to use this calculator

Choose karat or fineness and enter the mark you want to evaluate.
Enter the gross weight in grams and deduct any separately measured stones or non-metal parts.
Review fine grams, alloy grams and the comparison across common karats.

Worked example — illustrative inputs

A 10 gram item at 18K contains 7.5 grams of fine gold if the full weight is metal. Deducting 2 grams of stones first reduces the estimate to 6 grams.

Two ways to describe purity

Karat expresses gold purity on a nominal scale of 24. Fineness expresses precious-metal content in parts per 1,000. The worksheet translates both into the same fraction before multiplying by the net metal weight.

A hallmark and a fraction can differ

Fourteen divided by twenty-four is approximately 58.333%, while a 585 fineness mark represents 58.5%. Use the fineness value supported by the item specification or assay when precision matters. The calculator does not authenticate a hallmark or establish the composition of a plated item.

Read the purity comparison

Every row holds your net metal weight constant and changes only nominal karat. The chart shows fine grams, not market prices. Alloy grams are the remainder after the fine-gold fraction; no value is assigned to the other metals in the alloy.

Questions about this calculation

Should stones be counted in gold weight?

No. Deduct their measured mass and any other non-metal components before applying purity.

Can I use this for silver?

Fineness-to-fine-weight arithmetic also applies to silver and other alloys. The karat comparison is specifically a nominal gold convention.

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