Karat & Purity Calculator
Convert between karat, fineness and percent; see pure-gold content of any weight.
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What this tool does
Converts any gold purity between karat, fineness (parts per thousand) and percent. If you add a weight it also shows the pure-gold and alloy content, and the reference value when market data is available.
When to use it
Use it when a hallmark, assay certificate or quote uses a different purity scale from the one you work in.
What each input means
- Karat
- 24 karat is (nominally) pure gold; each karat is 1/24 of the total.
- Fineness
- Parts of gold per thousand: 750 = 18K, 916 or 917 = 22K, 999 = 24K.
- Weight (optional)
- Add a weight to see pure-gold content.
Formula and method
- Purity factor = karat ÷ 24
- Fineness = purity factor × 1000
- Percent = purity factor × 100
Worked example
Converting 22K:
- Purity factor = 22 ÷ 24 = 0.91667
- Fineness = 916.67 (often marked 916 or 917)
- Percent = 91.67%
22K = 91.67% = 916.7 fineness
Limitations
- Nominal purities are calculated; the hallmark on a real item can legally differ slightly.
- Alloy colour (yellow, white, rose) is not determined by karat alone.
Data sources, update times and handling of stale data are described in the calculator methodology.
Frequently asked questions
What is the difference between karat and carat?
Karat (K) measures gold purity. Carat (ct) measures the weight of gemstones: 1 ct = 0.2 g.
Is 24K exactly 100% gold?
In practice 24K gold is about 99.9% (999 fineness) or better; 24K is the nominal pure grade.
Related tools
- Gold Value Calculator — Reference value of gold by weight and purity, with pure-gold content.
- Gold Price Calculator — Gold price per gram, 10 grams, tola, troy ounce and kilogram for any karat, in your currency.