Carat to grams.

Answer

1 carat = 200 milligrams = 0.2 grams. To convert carats to grams, multiply by 0.2. To convert grams to carats, multiply by 5. A 1.5 ct stone weighs 0.3 g.

Worked example

A 1.5 carat diamond: 1.5 x 200 mg = 300 mg = 0.3 g. In other jewelry units that is 0.1929 pennyweight, 4.6297 troy grains and 0.0096 troy ounces. A 5 g piece is 5 / 0.2 = 25 carats.

How it works

Grams = carats x 0.2. Carats = grams x 5. The metric carat of 200 mg was adopted in 1907. Other units use the troy system: 1 troy ounce = 31.1034768 g, 1 pennyweight = 24 grains = 1.55517384 g, 1 troy grain = 0.06479891 g. The momme used by pearl dealers is 3.75 g. Carat (ct, weight of gems) is different from karat (k, gold purity).

Sources and basis (opened 2026-10-08): Wikipedia, Carat (mass); Wikipedia, Troy weight; Wikipedia, Pearl.

FAQ

How many grams are in a carat?

One metric carat is 200 milligrams, which is 0.2 grams.

How many carats are in a gram?

Five. 1 g = 1,000 mg and 1 ct = 200 mg, so 1 g = 5 ct.

How many milligrams is a 0.5 carat diamond?

0.5 ct x 200 mg = 100 mg, or 0.1 g.

Is carat the same as karat?

No. Carat (ct) measures the mass of gemstones and pearls. Karat (k) measures gold purity in parts per 24.

What is a momme?

A Japanese unit still used by pearl dealers for loose pearls and strands. One momme is 3.75 g, or 18.75 carats.