Karat Purity Calculator
Enter a karat, a percentage or a fineness number and the other two fill in automatically, along with the grams of pure gold in 10 g. Use it to decode stamps like 916, 750, 585 or 375.
Karat and purity converter
How to use it
- Type in any one box: Karat (1 to 24), Purity % or Fineness (parts per thousand, the number stamped on most hallmarks).
- The other two boxes update instantly.
- The result line gives the karat, the gold and alloy percentages, and how many grams of pure gold are in 10 g of the metal.
The formulas
- Purity % = karat ÷ 24 × 100
- Karat = purity % × 0.24
- Fineness = purity % × 10
- Pure gold in a piece = weight × purity % ÷ 100
Worked examples
| Stamp | Calculation | Result |
|---|---|---|
| 916 | 916 ÷ 10 = 91.6%; 91.6 × 0.24 | 21.98K, sold as 22K |
| 875 | 87.5 × 0.24 | 21.00K |
| 750 | 75 × 0.24 | 18.00K |
| 585 | 58.5 × 0.24 | 14.04K |
| 417 | 41.7 × 0.24 | 10.01K |
| 375 | 37.5 × 0.24 | 9.00K |
A 12 g chain stamped 750 contains 12 × 75 ÷ 100 = 9 g of pure gold.
Interpreting stamps
- Why 916 and not 917? 22 ÷ 24 is 91.67%, but the hallmark grade is set at a minimum of 916 parts per thousand. Pricing on this site uses 0.916. More in 916 gold meaning.
- 585 versus US 14K. Europe and India mark 14K as 585 (58.5%); US 14K is made to 14/24, about 58.3%. See 14K gold price.
- Stamps that are not purity: GF (gold-filled), GP, GEP, HGE and RGP mean a thin gold layer over base metal. The number beside them gives the karat of the layer only.
- Unusual grades such as 958 (23K), 833 (20K) or 990 can be decoded the same way.
- A stamp is a claim, not proof. For unmarked or doubtful items, see how to check gold purity; in India, check the HUID as explained in the BIS hallmark guide.
What purity means for value
The gold value of any piece is directly proportional to its purity. Ten grams of each common karat contain:
| Karat | Pure gold in 10 g | Value as share of 24K |
|---|---|---|
| 24K (999) | 10.00 g | 100% |
| 22K (916) | 9.16 g | 91.6% |
| 21K (875) | 8.75 g | 87.5% |
| 18K (750) | 7.50 g | 75.0% |
| 14K (585) | 5.85 g | 58.5% |
| 10K (417) | 4.17 g | 41.7% |
| 9K (375) | 3.75 g | 37.5% |
So if a jeweller tells you a piece is 22K but it tests at 20K (83.3%), it holds about 9% less gold than claimed (83.3 ÷ 91.6 = 0.909). Once you know the purity, value the piece with the gold calculator.
Frequently asked questions
What percentage of gold is 22K?
22 ÷ 24 = 91.67% in theory; hallmarked 22K must be at least 91.6% (916).
What karat is 750 gold?
750 means 75% gold, which is 18K.
Is 999 gold 24K?
Yes. 999 means 99.9% gold, the standard for 24K bars and coins. 999.9 is 99.99%.
What is the lowest karat sold as gold?
It depends on the country. In the US it is 10K; the UK hallmarks gold down to 9K (375).
What karat is 585 gold?
585 is 58.5% gold, which works out to 14.04K and is sold as 14K.