Gold Purity Chart

Karat purity chart

How the karat system works

Karat measures gold purity out of 24 parts. Pure gold is 24 karat, so a karat number divided by 24 gives the purity fraction: 18 divided by 24 is 0.75, or 75%. The remaining share of the alloy is other metals, usually copper, silver, zinc or nickel, mixed in to make the gold harder and more durable, since pure gold on its own is too soft for everyday jewelry that takes daily wear.

Don't confuse karat (a purity measure for gold specifically, abbreviated K or kt) with carat (a weight measure for gemstones, abbreviated ct). They sound identical and are easy to mix up, but they measure completely different things.

What a fineness stamp is, and why it matters

A fineness stamp is a three-digit number, like 585 or 750, stamped into the metal to show its purity in parts per thousand rather than in karats. 585 fineness means 585 out of 1000 parts are pure gold, exactly the same information as "14K", just expressed differently. Fineness stamps are more common on jewelry made outside the US, and on refined bars and coins, where an internationally recognized number avoids any karat-system ambiguity.

To convert a fineness stamp to a percentage for the calculator's custom purity field, just move the decimal point: 585 fineness is 58.5% pure, 750 fineness is 75.0% pure. The gold calculator page's karat dropdown already includes the standard karats, use custom purity for any fineness stamp that falls between them.

Worked example: converting a fineness stamp

Say a ring is stamped "916" rather than a karat number. That's 91.6% pure gold, equivalent to 22K. If the ring weighs 4 grams and the live gold price is $4,600 per troy ounce, the calculation is the same as any other karat: $4,600 divided by 31.1034768 grams per troy ounce gives about $147.89 per gram of pure gold, multiplied by 91.6% purity gives about $135.47 per gram, multiplied by 4 grams gives roughly $541.88 in melt value.

How the karat purity fractions in this chart were verified

The percentages and fineness stamps in the table above are the standard industry figures used by jewelers, refiners and precious metal dealers worldwide, they are not specific to this site. 24K is conventionally treated as 99.9% rather than a mathematically perfect 100%, since even "pure" refined gold retains a trace of other elements, this is why bullion is marked 999 rather than 1000. The other karats follow the same karat-divided-by-24 logic: 22 divided by 24 is 0.9167, rounded to the industry-standard 91.6% figure, 14 divided by 24 is 0.5833, rounded to 58.3%.

Common alloy metals mixed with gold at each karat

The remaining share of a karat-gold alloy (everything that isn't gold) is usually a mix of copper, silver, zinc, nickel or palladium, chosen for durability and color. Copper-heavy alloys push toward rose or red gold. Silver and palladium-heavy alloys push toward white or pale yellow gold. Because lower-karat items have more alloy metal by weight, they're generally harder and more scratch-resistant than higher-karat items, which is part of why 10K and 14K are popular for rings and other jewelry that takes daily wear, while 22K and 24K are reserved mostly for bullion and ceremonial jewelry that sees less physical stress.

Why 10K is the US legal minimum for "gold"

US federal law (enforced by the Federal Trade Commission) sets 10 karat as the minimum purity that can legally be marketed and sold as "gold" jewelry in the United States. Anything below that, including the 9K common in UK jewelry, cannot be labeled or sold as gold in the US market, even though it still contains real gold and still has real melt value. This is why 10K, 14K and 18K are the karats you'll see most often on US jewelry counters, while 21K, 22K and 24K are more associated with jewelry from South Asian, Middle Eastern and East Asian markets, where higher purity is culturally preferred and there's no equivalent minimum-karat law.