Find Purity From Gold Content
Fine-gold weight and total alloy weight determine the purity.
The calculation assumes the supplied pure-gold weight and total weight are measured consistently.
How Purity Is Calculated From Gold Content
When the amount of fine gold and the total alloy weight are both known, the gold percentage can be determined directly.
Once the percentage is known, the equivalent karat and fineness can also be calculated.
Fineness = Gold Fraction × 1,000
Example: 15 Grams Gold in 20 Grams Alloy
Suppose a material weighs 20 grams in total and laboratory or manufacturing information establishes that 15 grams of it is fine gold.
75% corresponds mathematically to 18K and 750 fineness.
Example: 9 Grams Gold in 10 Grams Alloy
90% × 24 ÷ 100 = 21.6K
90% × 10 = 900 fineness
This shows why the calculator is useful for measured or known gold-content data that does not necessarily begin with a conventional karat grade.
Purity Results From Common Ratios
| Fine Gold | Total Alloy | Gold % | Approx. Karat |
|---|---|---|---|
| 10 g | 10 g | 100% | 24K |
| 9.1667 g | 10 g | 91.67% | 22K |
| 7.5 g | 10 g | 75% | 18K |
| 5.8333 g | 10 g | 58.33% | 14K |
| 4.1667 g | 10 g | 41.67% | 10K |
| 3.75 g | 10 g | 37.5% | 9K |
Why This Calculator Is Different
This tool starts with an actual measured or known quantity of fine gold and the total material weight. It does not ask you to select an assumed karat. The purity is derived from the supplied gold-content ratio.
Gold Content and Alloy Balance
Once purity is known, the non-gold component can be calculated by subtracting fine-gold weight from total alloy weight.
For 15 grams of fine gold in 20 grams of total material, the remaining non-gold portion is 5 grams.
Important Limitations
The calculator assumes the supplied gold-content and total-weight measurements are accurate. It does not perform an assay or independently verify the composition.
If total weight includes gemstones, liquids, dirt, coatings or other non-relevant materials, the calculated purity will not represent the purity of the gold alloy itself.
Frequently Asked Questions
How do you calculate gold purity from gold content?
Divide pure-gold weight by total alloy weight and multiply by 100.
How do you calculate karat from gold content?
Calculate the gold fraction first, then multiply that fraction by 24.
If 15 grams of gold are in 20 grams of alloy, what is the purity?
15 ÷ 20 = 75%, corresponding mathematically to 18K and 750 fineness.
Can this calculator use different units?
Yes. The fine-gold and total weights can use the selected supported mass unit.
Does this calculator identify exact alloy metals?
No. It calculates overall gold proportion only.
Can this calculator authenticate jewellery?
No. It calculates purity from supplied measurements and cannot independently verify physical composition.