The concept
Weight, purity and a price per troy ounce
Gold is valued on three things: how much the piece weighs, how much of that weight is actually gold, and what a troy ounce of pure gold is trading for. This calculator keeps those three inputs separate so you can see which one moves the answer.
Karat tells you purity on a 24-point scale. A 14k piece is 14 parts gold in 24, about 58.3%. Fineness says the same thing per thousand: 585 is 14k, 750 is 18k, 999 is investment-grade bar gold. The rest of an alloy is silver, copper or other metals that add strength and colour but, for melt value, are treated as worth nothing.
To project what a gold holding could be worth years from now under an assumed price change, use the gold and commodity investment calculator. To see what a dealer might pay for pieces you want to sell, try the scrap gold calculator. The gold and commodity investing guide covers why gold prices are hard to model.
The method
How the calculation works
Weight in grams, purity as a fraction (karat ÷ 24), spot price in dollars per troy ounce. Other units are converted to grams first.
- Convert the weight to grams (1 troy ounce = 31.1035 g, 1 pennyweight = 1.5552 g, 1 everyday ounce = 28.3495 g).
- Subtract any stones or non-gold parts you entered.
- Multiply by purity to get grams of pure gold, then divide by 31.1035 for troy ounces.
- Multiply the troy ounces by the spot price you entered.
| Karat | Fineness | Gold content | Pure gold in 10 g |
|---|---|---|---|
| 8k | 333 | 33.3% | 3.33 g |
| 9k | 375 | 37.5% | 3.75 g |
| 10k | 417 | 41.7% | 4.17 g |
| 14k | 585 | 58.5% | 5.85 g |
| 18k | 750 | 75.0% | 7.50 g |
| 21k | 875 | 87.5% | 8.75 g |
| 22k | 916.7 | 91.7% | 9.17 g |
| 24k | 1000 | 100.0% | 10.00 g |
Frequently asked
Gold Calculator questions
How do I calculate the value of gold by weight?
Multiply the weight of the gold by its purity to get the weight of pure gold, convert that to troy ounces, then multiply by the spot price per troy ounce. For 10 grams of 14k gold, purity is 14 ÷ 24 = 0.583 (a stamped 585 gives 0.585), so there are about 5.85 grams of pure gold, or 0.188 troy ounces.
Where does the gold price in the calculator come from?
When available, the field is prefilled with a gold spot price from gold-api.com that this site caches and refreshes about twice a day, so it can be hours old and is shown with its timestamp. Gold trades continuously, so for a real transaction replace it with your dealer's live quote or the LBMA benchmark. If no recent cached price exists the field stays empty. Your own inputs are never sent anywhere.
What is the difference between a troy ounce and an ordinary ounce?
Gold is priced per troy ounce, which is 31.1035 grams. The everyday avoirdupois ounce is 28.3495 grams, so a troy ounce is about 10% heavier. Mixing the two up overstates or understates value by roughly that much.
How do I convert karats to purity?
Divide the karat by 24. 24k is pure gold, 18k is 75% gold, 14k is 58.3% and 10k is 41.7%. Many pieces are stamped with fineness instead, such as 585 for 14k or 750 for 18k, which is parts of gold per thousand.
Does this give me the price a buyer will pay?
No. It gives the melt value of the gold content. A buyer deducts for refining, risk and margin, so offers are normally below melt value, while jewelry with brand, craftsmanship or collector appeal can sell for more. The scrap gold calculator models a dealer's payout.
Should I subtract the weight of stones?
Yes. Gemstones, pearls, clasps with other metals and similar parts carry no gold. Weigh them out if you can, or enter an estimate in the non-gold weight field, and the tool removes that weight before applying purity.