Table of Contents
What Karat Tells you About Gold
Karat describes the share of gold in an alloy on a 24-part scale. It tells you about composition, rather than the total weight or finished price. The FTC’s gold-jewellery guidance explains that an 18K alloy contains 18 parts gold and six parts other metals. Read the karat label before selecting a price in the calculator.
| Label | Nominal fraction | Nominal gold share | Calculator use |
|---|---|---|---|
| 24K | Pure-gold reference | Check the declared product fineness | Pure-metal comparison |
| 22K | 22 ÷ 24 | About 91.67% | 22K alloy weight |
| 21K | 21 ÷ 24 | 87.5% | 21K alloy weight |
| 18K | 18 ÷ 24 | 75% | 18K alloy weight |
| 14K | 14 ÷ 24 | About 58.33% | Nominal 14K alloy weight |
| 10K | 10 ÷ 24 | About 41.67% | Nominal 10K alloy weight |
| 9K / 9ct | 9 ÷ 24 | 37.5% | 9ct / 375 alloy weight |
The table gives mathematical fractions for the karat labels. A physical article should be assessed against its actual specification and the applicable marking or testing scheme. Selecting a purity on a website does not test the item itself.
Fineness Marks: 999, 916 and 750
Fineness expresses metal content in parts per thousand. The UK hallmarking guidance explains this marking system. Mathematically, a 750 fineness is 75% gold, while 916 is 91.6%. A declared 999.9 specification is 99.99%, compared with 99.9% for 999.
Do not confuse a rounded karat fraction with an exact millesimal specification. For example, 22/24 is approximately 0.916667, while 916/1000 is exactly 0.916. When a publisher supplies a specific 916 reference, preserve its stated basis rather than silently replacing it with a differently defined calculation.
Calculate Fine-Gold Content Once
Multiply the alloy’s weight by its gold fraction to estimate the fine-gold weight. An 8-gram 18K article has nominal fine-gold content of 8 × 18/24 = 6 grams. A 10-gram 21K article has nominal fine-gold content of 8.75 grams. These are composition calculations; they do not include stones or a manufacturing premium.
You can reach the metal reference in either of two ways: multiply the full alloy weight by the matching-karat rate, or multiply its fine-gold weight by the pure-metal rate. Use one method consistently. Applying an 18K factor to a weight that already represents fine gold would reduce the amount twice.
A One-Ounce Gold Coin can Contain Alloy as Well
The US Mint’s 2025 one-ounce American Eagle specification identifies a 22K composition and one troy ounce of fine gold. The fine-gold quantity is already stated. For that specification, reducing the one-ounce fine-gold amount by 22/24 again would be the wrong calculation.
Read a coin or bar’s fine-metal content, total weight and purity as separate fields. Its collector value, condition, packaging or dealer premium can require a product-specific offer in addition to the metal calculation.
Compare the Total Item, Not Purity Alone
A lower-karat item has less gold than a higher-karat item of the same alloy weight. That does not establish which of two differently designed pieces has the lower selling price. Compare their metal weights and workmanship amounts, and keep stone values separate.
For an item offered as plated, filled or overlay, a solid-alloy calculation based on the whole object’s weight is unsuitable. FTC guidance distinguishes these descriptions from gold-alloy jewellery.
Continue with the gold calculator for a weight-specific result or the quotation guide for the full purchase comparison.
FAQs
Is 916 Exactly the Same Mathematical Value as 22/24?
No. They are close, but 916/1000 is 0.916 and 22/24 is approximately 0.916667. Use the fineness or reference actually specified. Small differences between a published purity table and a nominal ratio need not be a calculation error.
Is a Hallmark a Price Guarantee?
A hallmark relates to the article and the requirements of its scheme. It does not determine workmanship, a dealer’s margin or a resale offer. The country guide provides the appropriate primary references for checking marks in that market.
Which Input should I Use for a Mixed Collection?
Separate items by known purity and net alloy weight. Calculate each group at its matching reference, then add the results. A simple average of two karat labels gives the wrong answer when the groups have different weights.