Gold Karat Purity Calculator

Karat, fineness, and price

Karat measures how much of an alloy is pure gold, out of 24 parts. 24k is essentially pure (999 fineness, or 99.9%), 22k is 91.67%, 21k is 87.5%, and 18k is 75%. Fineness is just that purity expressed as a fraction, and the price per gram of a karat scales directly with it.

You can price from two bases. From the spot price, the tool converts the per-troy-ounce price of pure gold to a per-gram price, then multiplies by the karat's fineness. From a 24k per-gram price, it scales by the ratio of the target karat's fineness to 24k. Both give the metal value per gram before any making charge or dealer margin.

Worked example

At a spot price of $2,650 per troy ounce, pure gold is about $85.20 per gram (2,650 / 31.1034768). Multiplying by fineness gives roughly $63.90/g for 18k (75%), about $78.11/g for 22k (91.67%), and about $85.11/g for 24k (99.9%). Switch the basis to a known 24k gram price and every other karat scales from it in the same proportions.

Common mistakes

This is the pure metal value only. Retail jewellery prices add a making charge, wastage, and dealer margin on top, so a shop price per gram will be higher. Also confirm the local fineness convention — 22k is treated as 91.67% here, but some markets hallmark 22k slightly differently.