Carats to Grams (ct to g)

1 carat equals 0.2 grams exactly.

1 carat = 0.2 grams

How to convert carats to grams

To convert carats to grams, multiply the number of carats by 0.2. This factor is exact. To go the other way, multiply grams by 5.

grams = carats × 0.2

Example: 10 carats = 2 grams.

About these units

Carat (ct)

Metric (SI)Current unit

Exactly 200 milligrams. The unit for weighing gemstones such as diamonds. Not to be confused with the karat, a measure of gold purity.

Jewellers once weighed stones against seeds. The word carat traces back to the Greek keration, meaning a carob seed, and reached English through Italian and Arabic. Carob seeds were used as balance weights for gems and gold, though their mass varies about as much as any seed does. Before 1907 each country had its own carat, ranging from roughly 187 to 216 milligrams. It was used for gold early on and for diamonds from the 1570s. An international carat of 205 mg was proposed in Paris in 1871, but the 200 mg metric carat won out.

The metric carat was adopted at the Fourth General Conference on Weights and Measures in 1907. France made it mandatory, the United States followed in 1913 and the United Kingdom in 1914. Today it is exactly 200 mg, so five carats make a gram, and it is divided into 100 points of 2 mg each; a diamond described as 25 points is a quarter carat. Carat is used for gemstones and pearls, and it should not be mixed up with karat, which measures the purity of gold and is a separate idea.

1 carat = 0.0002 kilograms (exactly).

Sources: Wikipedia: Carat (mass); NIST Guide to the SI, Appendix B.8 (mass conversions)

Gram (g)

Metric (SI)Current unit

One thousandth of a kilogram. The standard unit for food quantities and small objects.

A gram was once defined as a small drop of the natural world. The French National Convention of 1795 set it as the absolute weight of a volume of pure water equal to a cube one hundredth of a metre on each side, a cubic centimetre. The reference temperature was first the melting point of ice and was later changed to the temperature of maximum density of water, about 4 degrees Celsius. The word came into French as gramme, from Late Latin gramma, itself from the Greek for a letter or small mark; in Late Antiquity it meant about one twenty-fourth of an ounce.

The gram was the base unit of mass in the centimetre-gram-second system, but in 1960 the SI took the kilogram as its base unit, which made the gram one thousandth of it. That is why it appears in so many everyday places: it is the standard for non-liquid ingredients in cooking and shopping, and nutrition labels commonly list contents per 100 g. For a sense of scale, a small paper clip or a pen cap weighs about a gram, and a Japanese 1-yen coin is close to exactly that, while a US penny is around 2.5 g.

1 gram = 0.001 kilograms (exactly).

Sources: Wikipedia: Gram; Wikipedia: Kilogram

Related conversions

See all weight & mass units.