How Gold Price Per Gram Is Calculated
Every number here is derived, not quoted: a live spot price per troy ounce, divided into grams and multiplied by the purity of the karat. The constants are below so you can check any figure by hand.
Spot prices are supplied by Gold API and cached for 30 seconds. Current historical periods update every minute. Today’s change compares the latest price with the UTC day’s opening price; quote times display in your local time.
Historical charts show hourly averages for 24H, weekly averages for 5Y and MAX, and daily averages for other ranges. Weekly points average the available daily averages. Average is the arithmetic mean of available period averages. The table and range highs and lows use actual OHLC data. Availability follows the provider. we do not fill missing dates with invented prices. 24K estimates default to 999 fineness (99.9%); an explicit fineness takes precedence over nominal karat values.
The calculation
Divide the spot price by the number of grams in a troy ounce.
Multiply by the karat’s fine-gold fraction (karat ÷ 24). A millesimal stamp reads directly: 585 means 0.585.
Your weight is converted to grams, then any non-gold weight you declare (stones, clasps, movements) is subtracted. Only the remaining metal is priced.
Purity and unit constants
| Karat | Fine gold | Stamp |
|---|---|---|
| 24K | 99.9% | 999 |
| 22K | 91.67% | 916 |
| 21K | 87.5% | 875 |
| 18K | 75% | 750 |
| 14K | 58.33% | 585 |
| 10K | 41.67% | 417 |
| Unit | In grams |
|---|---|
| 1 troy ounce (oz t) | 31.1034768 g |
| 1 pennyweight (dwt) | 1.55517384 g |
| 1 ounce, avoirdupois | 28.349523 g |
| 1 tola | 11.6638 g |
| 1 kilogram | 1000 g |
Karat purity is the exact fraction of 24, so 14K is 58.33%, not the 58.5% a 585 stamp implies. Enter a stamp and the stamped value is used.
Jewellery is quoted in grams or pennyweight, bullion in troy ounces. A kitchen scale’s avoirdupois ounce is 8.7% lighter, a common source of overestimates.