Convert gold karats to purity percentage or fineness, reverse percentage to karats, and calculate pure-gold and alloy weight in common jewelry units.
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Karat to Percentage Formula
The following formula is used to convert karat to percentage.
Variables:
- P is the percentage of gold purity
- K is the karat value of the gold
To calculate nominal gold purity, divide the karat value by 24 and multiply by 100. Fineness is parts per 1,000: divide it by 10 to obtain percent. Exactly 14/24 is 58.3333…%, while a 585 fineness mark specifies 58.5%; exactly 22/24 is 91.6667…%, while 916 specifies 91.6%. The table uses exact nominal karat fractions, not legal hallmark thresholds. Birmingham Assay Office explains common fineness marks.
| Karat (K) | Gold Purity (%) |
|---|---|
| 1K | 4.17% |
| 2K | 8.33% |
| 3K | 12.50% |
| 4K | 16.67% |
| 5K | 20.83% |
| 6K | 25.00% |
| 8K | 33.33% |
| 9K | 37.50% |
| 10K | 41.67% |
| 12K | 50.00% |
| 13K | 54.17% |
| 14K | 58.33% |
| 15K | 62.50% |
| 16K | 66.67% |
| 18K | 75.00% |
| 20K | 83.33% |
| 21K | 87.50% |
| 22K | 91.67% |
| 23K | 95.83% |
| 24K | 100.00% |
| Formula: Percentage = (Karat / 24) × 100. 24K = 100% pure gold; 1K ≈ 4.1667%. | |
What is Karat?
Karat is a unit of measurement used to describe the purity of gold alloys. On the ideal arithmetic scale, 24/24 is 100% gold. Actual measured or marked fineness can be lower; 999 fineness, for example, is 99.9%. When gold is mixed with other metals to create an alloy, the karat value decreases. For example, 18-karat gold is 75% gold and 25% other metals. The higher the karat value, the greater the proportion of gold in the alloy.
How to Calculate Karat to Percentage?
The following steps outline how to calculate the percentage of gold purity from the karat value.
- First, determine the karat value of the gold (K).
- Next, use the formula P = (K / 24) * 100 to calculate the percentage of gold purity.
- Finally, check your answer with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
Karat value of the gold (K) = 18
Percentage of gold purity (P) = (18 / 24) * 100 = 75%. For 10 g of a uniform 18K alloy, modeled gold mass is 7.5 g and other-alloy mass is 2.5 g. Exclude stones and non-alloy components; a plating or gold-filled mark does not make the whole item that purity. Mass conversions use 1 troy ounce = 31.1034768 g and 1 pennyweight = 1.55517384 g.
