A gold purity calculator for karat, percentage and fineness
Gold purity is written three ways: in karats (22K), as a percentage (91.67%) and as fineness in parts per thousand, the number stamped in a hallmark (916). This gold purity calculator converts between all three, tells you which standard grade a number matches, and works out how much pure gold a piece of any weight contains.
It also answers the jeweller’s question in reverse: how much alloy to add to bring gold down to a lower karat, or how much fine gold to add to raise it. A karat chart shows every common grade side by side with the pure-gold content for your weight. The calculation is instant and runs in your browser.
How to use the Gold Purity & Karat Converter
- Choose what you know: Karat, Purity % or Fineness — or tap a common karat.
- Type the value, for example 22, 91.6 or 916.
- Optionally enter the weight of the piece and its unit (grams, tola, troy ounces, pennyweight…).
- Open Change the purity to enter a target fineness and see the alloy or fine gold to add.
- Read the conversion, the nearest standard grade and the pure gold content, and copy the result.
Gold Purity & Karat Converter features
Three-way conversion
Karat, per cent and fineness from any one of them.
Grade matching
Says whether the number matches a standard grade such as 916 or 585, or how far it is from the nearest one.
Pure gold content
Grams of pure gold and alloy in a piece of any weight and unit.
Alloying maths
Alloy needed to lower the karat, or fine gold needed to raise it.
Karat chart
Nominal purity and hallmark fineness from 24K to 9K, with pure content for your weight.
Gold purity formulas
Purity % = karat ÷ 24 × 100— 22K is 22 ÷ 24 = 91.67%; 18K is 75%; 14K is 58.33%.Fineness = purity × 1,000— 91.67% is 916.7; hallmarks round to standard grades such as 916.Karat = fineness ÷ 1,000 × 24— 585 is 14.04K, 750 is 18K.Pure gold = weight × purity— 10 g of 22K holds 9.167 g of pure gold.- Lowering purity p1 to p2:
add alloy = weight × (p1 ÷ p2 − 1). Raising with gold of purity pf:add gold = weight × (p2 − p1) ÷ (pf − p2).
Hallmark grades and why 22K is 916
India’s hallmarking standard (BIS IS 1417) sets the grades 24K (999 and 995), 23K (958), 22K (916), 20K (833), 18K (750), 14K (585) and 9K (375). 22 ÷ 24 is 916.67, and 14 ÷ 24 is 583.3, so the hallmark numbers are rounded grades: 916 is a hair below the nominal 22K and 585 a little above the nominal 14K. Every hallmarked piece also carries a six-character HUID that can be checked in the BIS Care app.
Worked example: a 10 g 22K chain contains 9.167 g of pure gold (9.16 g at the 916 grade). To turn it into 18K for a stronger setting, add 10 × (0.9167 ÷ 0.75 − 1) = 2.222 g of alloy, giving 12.222 g of 18K. Going the other way, 10 g of 18K needs 20 g of 999 gold to reach 916.
To price a piece, use the gold rate calculator (making charges and GST) or, for scrap, the melt value calculator.
Gold Purity & Karat Converter FAQ
How do you calculate gold purity from karat?
Divide the karat by 24. 22K ÷ 24 = 0.9167, or 91.67% pure gold. The gold purity calculator also gives the fineness (916.7) and the pure gold in your piece.
What does 916 mean on gold?
It is the fineness: 916 parts of pure gold per 1,000, the BIS hallmark grade for 22-karat gold.
What is the purity percentage of 18K gold?
18 ÷ 24 = 75%, hallmarked as 750. The other 25% is alloy such as silver and copper.
Is 14K gold 58.3% or 58.5%?
Nominally 14 ÷ 24 = 58.33%. The common hallmark grade is 585 (58.5%), slightly above the nominal value.
How much pure gold is in 10 grams of 22K?
10 × 0.9167 = 9.167 g nominally, or 9.16 g at the 916 grade.
Can this calculator test my gold?
No. It converts numbers; to know real purity, have the piece tested by a BIS-recognised hallmarking centre or an assayer.