Karat describes gold as parts out of 24. An 18K alloy is nominally 18/24, or 75%, gold. Fineness describes parts per thousand: a 750 mark describes the same nominal proportion. Neither label measures the weight of the item.
Common purity levels
| Mark | Nominal gold share |
|---|---|
| 9K | 37.5% |
| 10K | 41.6667% |
| 14K | 58.3333% |
| 18K | 75% |
| 22K | 91.6667% |
| 24K | 100% theoretical |
Some marked fineness standards differ slightly from exact K/24 arithmetic. A 585 mark is 58.5%, whereas exact 14/24 is 58.3333%. Use a fineness input, such as the one in the gold purity calculator, when a verified assay or marking gives that figure. A 999.9 bar is 99.99%, not mathematically 100%.
A worked example
Suppose an 18K item contains 12 grams of metal, excluding stones. Its nominal fine-gold content is 12 × 18/24 = 9 grams. At a hypothetical fine-gold reference of USD 100 per gram, its contained-gold value would be USD 900. A buyer may offer less after refining, testing, operating costs and margin. The scrap gold payout calculator models those deductions.
What the calculator cannot establish
A stamp is not an assay. Gold plating, filled products, solder and non-gold components complicate valuation. Do not apply solid-gold arithmetic to the full weight of a plated item. Our calculator estimates contained metal only and does not authenticate jewellery or include artistic, collectible or brand value.
Open the gold calculator and choose either a karat preset or a custom fineness. For the underlying price and observation date, see the gold reference page.
Test yourself. Check what you learned with the precious metals essentials quiz: 5 quick questions, each with a short explanation.
Sources & further reading
Educational reference. How we create and review our content.
