Karat Conversion Calculator
Karat, fineness and percentage gold.
Convert gold purity between karat, fineness in parts per thousand and percentage, with the hallmark numbers each corresponds to.
Purity
18.0k
750.0 parts per thousand
Hallmarks round down to a standard figure, because a piece must be at least as pure as its mark: 14k is exactly 583.3 and is stamped 585, 22k is 916.7 and stamped 916. Karat tells you how much gold is present, not what colour it is — that depends on what the remaining alloy is.
How the Karat Conversion Calculator works
Karat is a plain fraction: it counts twenty-fourths of pure gold, so 18k is eighteen parts gold to six parts alloy, or 750 parts per thousand. The hallmark numbers stamped on jewellery are those fineness figures rounded down — 14k works out at 583.3 and is stamped 585, 22k is 916.7 and stamped 916.
Also known as: gold purity calculator · gold fineness converter · carat gold calculator
Karat is a fraction, not a grade
Karat counts twenty-fourths of pure gold by weight. Eighteen karat is eighteen parts gold to six parts other metal, which is 750 parts per thousand or 75%. Nine karat is 375, fourteen is 583.3 and twenty-two is 916.7.
Hallmarks round those figures to a standard number, and they always round in the same direction: down to a mark the piece can honestly meet. Fourteen karat is stamped 585 rather than 583, twenty-two karat 916 rather than 917. A piece must be at least as pure as its mark, never less.
The word carat, spelled that way, is a weight for gemstones and has nothing to do with gold purity. Karat with a k is purity; carat with a c is 0.2 grams.
A worked example
A ring marked 585 is 58.5% gold. If it weighs 6 grams, it contains 3.51 grams of gold and 2.49 grams of alloy — usually copper and silver, sometimes with palladium or nickel in white gold.
The same 6 gram ring in 18k would contain 4.5 grams of gold. That is a 28% difference in gold content for a mark most people read as a small step, which is why karat matters far more to value than it does to appearance.
Where the answer misleads
Higher karat is purer, not better. Pure gold is soft enough to deform in daily wear, so 24k is a poor choice for a ring. Eighteen karat balances colour and durability; fourteen and nine are harder still and hold stones more securely, which is why they dominate in engagement rings.
Karat also says nothing about colour. The same 18k can be yellow, white or rose depending entirely on what the remaining 25% is. White gold is usually rhodium plated on top of that, and the plating wears off and needs redoing every few years — a maintenance cost the karat mark does not hint at.
Finally, plated and filled items carry marks that look similar and mean something entirely different. Gold filled is a bonded layer measured in percentages of total weight; gold plated is microns thick. Neither has meaningful scrap value.
Frequently asked questions
What does 585 mean on gold?
585 parts per thousand gold, which is 14 karat. The exact figure is 583.3, and the hallmark rounds to 585 because the piece must be at least as pure as its mark. Similarly 750 is 18k and 375 is 9k.
How do I convert karat to a percentage?
Divide by 24 and multiply by 100. 18k is 18/24, which is 75% gold. 14k is 58.3%, 9k is 37.5% and 22k is 91.7%.
Is higher karat always better?
Purer, not better. Pure gold is soft enough to deform in wear, so 24k is unsuitable for a ring that gets worn daily. 18k balances colour and durability; 9k and 14k are harder still and hold stones more securely.
Does karat affect the colour?
The alloy does. The same 18k can be yellow, white or rose depending on whether the 25% that is not gold is silver, copper, palladium or nickel. Karat tells you how much gold is present, not what it looks like.