🏅 Gold Karat & Purity Calculator
Convert gold karat to purity percentage and fineness, or reverse a purity percentage back to karat — instant, exact answers for everything from 10k to pure 24k.
🔁 Karat ⇄ Purity ⇄ Fineness
What is a Gold Karat & Purity Calculator?
It converts between the three ways gold purity is expressed: karat (in 24ths), purity percentage, and millesimal fineness. Enter a karat to see its percentage and fineness, or reverse it to turn a hallmarked percentage back into karats.
Use it to decode a hallmark, compare 14k and 18k pieces, or understand what a "750" stamp means before you buy. Purity is exactly what drives a gold item's metal value, so pair this with the gold value calculator to estimate what a piece is really worth.
❓ Frequently Asked Questions
How do karat, purity, and fineness relate?
Karat measures gold purity in 24ths. Purity percentage is karat ÷ 24 × 100, and fineness is the same figure per thousand. So 18k is 18/24 = 75.00% pure, or 750 fineness; 22k is 91.67% (916.67); and 14k is 58.33% (583.33).
Can I convert a purity percentage back to karat?
Yes — switch the tool to reverse mode and enter a purity percentage, and it returns the equivalent karat as percent ÷ 100 × 24. For example 75% maps to 18k and 100% to 24k. This is handy when a hallmark shows a fineness or percentage rather than a karat stamp.
What do common gold hallmarks like 750 or 585 mean?
They're millesimal fineness stamps — parts of pure gold per thousand. 999 is 24k, 916 is 22k, 750 is 18k, 585 is 14k, and 375 is 9k. If you find one of these numbers inside a ring or on a bracelet, it's telling you the gold's purity directly.
Is 24k gold ever used for everyday jewelry?
Rarely. Pure 24k gold is soft and scratches or bends easily, so jewelry is usually alloyed down to 18k, 14k, or 10k for durability, with the karat balancing colour and richness against strength. Investment bars and coins, by contrast, are typically near-pure.