Carats ⇄ grams converter

1 carat = 0.2 grams, exactly

The metric carat is precisely 0.2 grams, or 200 milligrams. This value was fixed internationally in 1907 to put an end to centuries of diverging local definitions. Our converter lets you move instantly from one unit to the other, in both directions.

Where does the word “carat” come from?

From the seed of the carob tree. In Mediterranean antiquity, gem merchants used these seeds as counterweights because they were thought to have a remarkably constant weight. The story is charming; the truth, revealed by modern studies, is that carob seeds vary as much as any other seed — the merchants were mistaken, but the name stuck.

The absolute trap: two different carats

Beware: there are two “carats” that have nothing to do with each other, and the confusion is expensive.

The carat of weight (ct) measures a gem's mass: a 1.5-carat diamond weighs 0.3 grams. The karat of purity (K or kt) measures the proportion of gold in an alloy, out of 24: 18-karat gold contains 18/24 pure gold, or 750 parts per thousand — the familiar “750” stamp, or the eagle's head hallmark in France. A piece can therefore perfectly well be “18-karat gold set with a 1-carat diamond”: the two figures refer to entirely different things.

Worth knowing in practice: a cut gem's weight is always given in carats, while a rough stone or collection specimen is usually weighed in grams. And for very small stones, one speaks in points: 1 point = 0.01 carat, so a “25-point” diamond weighs 0.25 carats.