Calculator
Gold Purity Calculator
Convert any karat or fineness number into the equivalent gold percentage and value, and check the BIS HUID standard.
What does "purity" mean for gold?
Gold purity is expressed in two equivalent ways: the karat scale (parts per 24) and the fineness scale (parts per 1000). 24-karat gold is 99.9% pure (fineness 999); 22-karat is 91.6% pure (fineness 916); 18-karat is 75% pure (fineness 750). The non-gold portion is alloy — usually copper, silver, or zinc, added for hardness and colour.
BIS hallmark and HUID
Every piece of gold jewellery sold in India must carry a BIS hallmark consisting of the BIS logo, the purity number (916 or 750 etc.), the jeweller's identification mark, and a 6-digit Hallmark Unique ID (HUID). You can verify the HUID through the BIS Care app on your phone — it tells you the karat, weight, and registration of the piece against the official BIS database.
How jewellers test purity
- Karatmeter (X-ray fluorescence): Non-destructive, gives a digital readout of karat. Standard at large jewellers.
- Touchstone test: Traditional method, scratches the gold against a touchstone and applies acid; less accurate but still used.
- Acid test: Destructive, used for buyback testing; multiple acids of different strength applied to a tiny scratch.