Gold alloy and karat.

Answer

Fine gold in a piece = weight x karat / 24. A 10 g piece of 14k holds 5.833 g of fine gold and 4.167 g of alloy metal. Melting pieces together gives total fine gold / total weight x 24: 5 g of 10k with 3 g of 18k comes out at 13.00k.

Worked example

10 g of 14k: 10 x 14/24 = 5.833 g of fine gold and 4.167 g of other metals. Melting 5 g of 10k (2.083 g gold) with 3 g of 18k (2.250 g gold) gives 4.333 g of gold in 8 g, and 4.333 / 8 x 24 = 13.00 karat (54.17% gold).

How it works

Fine gold = weight x karat / 24. Blended karat = (sum of weight x karat) / total weight. Karat is parts of gold per 24 by mass, so a blend is a weighted average. Use the same unit for every weight. This assumes each piece is exactly its stated karat and loses no metal in melting; real stamps are rounded standard values and refining losses are not modelled.

Sources and basis (opened 2026-10-08): Wikipedia, Fineness.

FAQ

How much pure gold is in 14k gold?

14/24 or 58.33% of the weight. A 10 g piece holds 5.833 g of pure gold.

What karat do I get melting 10k and 18k together?

It depends on the weights. Equal parts give 14k. 5 g of 10k with 3 g of 18k gives 13.00k.

How much alloy metal is in 18k gold?

6/24 or 25% of the weight is non-gold metal such as copper or silver.

Can I make 18k by adding fine gold to 14k?

Yes. Add fine gold until total fine gold / total weight reaches 0.75. Enter your pieces, including a 24k piece, in the blend to test the result.

Is the result exact?

It is exact arithmetic on stated karats. Real jewelry is stamped to rounded standards and melting can lose small amounts of metal.