As mentioned above, 24 karat gold is the highest possible number in pure gold, but it is often mixed with other metals to create alloys that are more durable and more suitable for everyday wear in jewelry. The more an alloy is mixed with pure gold, and therefore the less gold there is, the lower the number of karats.
Gold is most often mixed with either silver, zinc, copper, or palladium, creating a different number of karats and different colors of gold, such as rose gold or white gold.
Traditional karats used in gold jewelry number from pure gold at 24k, 22k, 18k, 14k or 10k.
Below is a chart that explains the conversion figures of gold from percentages and decimals to karats.
| Number of Karats | Fraction of Gold | % of Gold Purity | Millesimal fineness |
| 9K | 9/24 | 37.5 | 375 |
| 10K | 10/24 | 41.7 | 416/417 |
| 12K | 12/24 | 50.0 | 500 |
| 14K | 14/24 | 58.3 | 583/585 |
| 18K | 18/24 | 75.0 | 750 |
| 22K | 22/24 | 91.7 | 916/917 |
| 24K | 24/24 | 99.9 | 999 |