Gold Karat to Purity Converter
Convert gold karats to purity percentage, fineness and hallmark stamp — or enter a percentage or fineness value to get the karat equivalent. Just pick your input type and enter the number.
Convert Karats to Gold Purity Percentage
Gold Purity
Where:
- \(K\) — karat value (0 to 24)
- \(P\) — gold purity percentage by mass
- \(F\) — fineness, parts of gold per thousand
One karat means 1 part in 24 is pure gold, so 24 kt is pure gold. The three ways of expressing purity — karat, percentage and fineness — are simply different ways of writing the same fraction of gold by mass.
Gold Purity – Calculation Example
Example: you have a 14 kt gold ring and want to know its purity, fineness and hallmark stamp.
\[ P = \frac{14}{24} \times 100 = 58.33\% \]
\[ F = \frac{14}{24} \times 1000 = 583.3 \]
Result: 14 kt gold is 58.33% pure gold, fineness 583.3, stamped as 585. The remaining 41.67% is alloy metal such as silver, copper or zinc.
How to Use the Gold Purity Calculator
- Open the dropdown “Your input is a” and choose what your number represents: Karat value, Purity percentage or Fineness.
- Enter the number in the “Gold karat / purity value” field — for example 14 for 14 karat, 58.5 for a percentage, or 585 for fineness.
- Read the results: Gold purity in %, Fineness in parts per thousand, the Karat equivalent, and the Millesimal hallmark stamp you would expect on the piece.
- Check the comparison table below the results to see how your value stacks up against the common karat grades from 9 kt to 24 kt.
What Does Gold Purity Mean?
Gold purity describes how much of a metal's mass is actually gold. Pure gold is soft and easily scratched, so it is almost always mixed with other metals — typically silver, copper, zinc, nickel or palladium — to make it harder, cheaper and sometimes to change its colour. The more gold in the alloy, the higher the purity and the more the piece is worth.
There are three common ways to express purity. The karat (kt) system counts parts of gold out of 24: 12 kt is half gold, 24 kt is pure. The percentage system states the gold content directly, so 18 kt = 75%. The fineness or millesimal system counts parts of gold per 1000: 18 kt = 750, 14 kt = 585. This last number is what you find stamped inside most jewellery sold in Europe and much of the world, which is why hallmark stamps like 375, 585, 750 and 916 are worth recognising.
A higher karat number does not automatically mean "better". 24 kt gold is very soft and bends or scratches easily, which makes it poorly suited to rings worn every day. Most durable everyday jewellery is 14–18 kt, which keeps a rich colour while holding up to wear. Investment bars and coins, on the other hand, are almost always 99.9% fine gold (24 kt, stamped 999).
When interpreting the result, remember that purity is measured by mass, not by volume. The alloy metals in lower-karat gold also change the density and colour of the piece. If you need to work with the physical properties of the metal, our density unit converter can help with the units involved.
Assumptions, Limitations and Practical Tips
- Mass basis: the calculator assumes purity is measured by mass, which is the standard convention for gold hallmarking worldwide.
- Rounding of stamps: millesimal hallmark stamps are normally rounded to the nearest 5 or 10, so 14 kt (583.3) is stamped 585. The calculator follows this convention.
- Valid ranges: karats run from 0 to 24, percentage from 0 to 100, and fineness from 0 to 1000. Values outside these ranges are physically meaningless for gold alloys.
- Plating is not included: a gold-plated or gold-filled item may carry a karat mark describing only the thin surface layer, not the whole piece. The calculator cannot detect this — only a proper hallmark or assay can.
- Regional differences: the legal minimum to be sold as "gold" varies: 9 kt in the UK, 10 kt in the US, and 14 kt or higher in many countries in Asia and continental Europe. Always check local rules when buying or selling.
- Colour is not purity: white, rose and yellow gold of the same karat contain the same gold percentage; the difference comes from the alloy metals, not the purity.
If you are buying a gold ring, you may also find our ring size converter useful, and if you work with other "parts per" measurements, the PPM to percent converter covers similar conversions for liquids and gases.
Frequently Asked Questions
How do I convert karat to percentage by hand without a calculator?
Divide the karat number by 24 and multiply by 100. For example, 18 kt: \( 18 \div 24 = 0.75 \), then \( 0.75 \times 100 = 75\% \). To get fineness, multiply by 1000 instead, so 18 kt = 750 parts per thousand. Any karat value can be converted this way — the math is always the same simple fraction of 24.
What is the difference between karat and carat?
Karat (kt) measures gold purity — how many parts out of 24 are gold. Carat (ct) measures the weight of gemstones, equal to 0.2 grams. They are unrelated: a 1 carat diamond can be set in 18 karat gold. The spelling overlaps in some countries, which causes confusion, so check whether the number refers to metal purity or stone weight.
Why is 14 kt gold stamped 585 and not 583?
14 kt equals 583.3 parts per thousand mathematically, but hallmarking conventions round stamps to the nearest 5 or 10. Rounding 583.3 up gives the familiar 585 mark. The same happens with other grades: 22 kt (916.7) is stamped 916, and 10 kt (416.7) is stamped 417. The stamp is a conventional mark, not an exact measurement.
What does a 916 or 750 stamp on jewellery mean?
These are millesimal fineness marks: 916 means the piece is 916 parts gold per 1000, which is 91.6% pure or 22 kt. 750 means 75% gold, or 18 kt. Other common stamps include 375 (9 kt), 417 (10 kt), 585 (14 kt) and 999 (99.9% pure gold). The stamp tells you the gold content of the alloy by mass.
Is 24 karat gold 100% pure?
Almost, but not exactly. By convention 24 kt refers to pure gold, yet in practice even investment-grade bullion is 99.9% (999) or 99.99% (9999) fine, because removing every last trace of impurity is impractical. Jewellery marked 24 kt is typically 99% gold or higher. For all everyday purposes, 24 kt and "fine gold" mean the same thing.
Can a karat value be higher than 24?
No — 24 is the maximum because the karat scale is defined as parts of gold out of 24 total parts. A value above 24 would mean more than 100% gold, which is impossible. If you see a number like 999 or 750 on a piece, that is fineness, not karat; divide by 1000 and multiply by 24 to get the karat equivalent (999 ≈ 23.98 kt).
Does the karat mark tell me how much the piece is worth?
Only partially. The karat tells you the gold content, but value also depends on the total weight, the current gold price, craftsmanship and any gemstones. A heavy 9 kt chain can contain more gold than a tiny 18 kt ring. To estimate melt value, multiply the piece's weight by the purity percentage, then by the current gold price per gram. For valuable items, get a professional appraisal.