24K, 22K, 18K and 14K gold: purity explained

Karat and fineness measure the same underlying property

The theoretical gold fraction is the karat number divided by 24. Fineness instead expresses the fraction in parts per thousand. An 18K item has a nominal gold content of 75%, corresponding to 750 fineness.

Real products are often identified by fineness marks such as 585, 750 or 999. A stamp is information about the claimed purity, not a substitute for verifying the item. Standards and accepted tolerances vary across markets.

The factors used by our calculator

These approximate factors preserve this site’s calculator convention. For example, theoretical 14/24 is about 58.33%, while a 585-marked product claims 58.5%. A purity selection therefore estimates value rather than certifying a particular product.

Use purity when estimating gold content

For an illustrative 20-gram item with 750 fineness, the fine-gold weight is 20 × 0.750 = 15 grams, provided the quoted weight represents the gold alloy alone. Multiplying 15 by the pure-gold gram reference gives the estimated metal value.

The finished item can sell for a different amount. Design, fabrication, brand, stones, distribution and local charges are outside this metal-only calculation. If buying or selling an item, request its net weight, fineness and an itemised quote.