Carats to Grams Converter (ct to g)
1 ct = 0.2 g exactly (200 mg). Convert carats to grams for diamonds and gemstones, with ct to g and g to ct charts and diamond points explained.
Gram (g) = Carat (ct) × 0.2
Carat (ct): The metric carat is exactly 200 milligrams and is used worldwide to weigh diamonds and other gemstones. It is unrelated to the karat that measures gold purity.
Gram (g): The gram is one thousandth of a kilogram, the SI base unit of mass. It is used worldwide for food, postage and small quantities of almost anything.
| Carat (ct) | Gram (g) |
|---|---|
| 1 | 0.2 |
| 5 | 1 |
| 10 | 2 |
| 25 | 5 |
| 50 | 10 |
| 100 | 20 |
Diamonds and other gemstones are weighed in metric carats, and a metric carat is defined as exactly 200 milligrams, or 0.2 g. The definition was agreed internationally in the early 20th century to replace older carats that differed from one trading center to another, so a 1 ct stone now weighs the same everywhere.
The carat is a unit of mass, not size, and it has nothing to do with the karat that measures gold purity. Jewelers also divide the carat into 100 points, so a 50-point diamond is half a carat, 0.1 g. The second chart turns gram readings from a scale back into carats.
How to use this tool
- Type a value in the Carat box to see it in grams, or type in the Gram box to convert the other way.
- Press ⇄ to swap the two units, or Load example for a typical value.
- Check the charts below for common values; for other units, open the Weight & Mass converter.
Formula
Gram (g) = Carat (ct) × 0.2
Carat (ct) = Gram (g) × 5
Both factors come from exact definitions: 1 gram = 5 carats and 1 carat = 0.2 grams (shown to 12 significant digits).
Example
Two conversions worked with the same factors the converter uses:
1.5 ct × 0.2 = 0.3 g
1 g × 5 = 5 ct
Carat to Gram chart
Common values from carats to grams, rounded to four decimal places.
| Carat (ct) | Gram (g) |
|---|---|
| 0.01 | 0.002 |
| 0.05 | 0.01 |
| 0.1 | 0.02 |
| 0.25 | 0.05 |
| 0.33 | 0.066 |
| 0.5 | 0.1 |
| 0.7 | 0.14 |
| 0.75 | 0.15 |
| 0.9 | 0.18 |
| 1 | 0.2 |
| 1.25 | 0.25 |
| 1.5 | 0.3 |
| 2 | 0.4 |
| 2.5 | 0.5 |
| 3 | 0.6 |
| 4 | 0.8 |
| 5 | 1 |
| 10 | 2 |
| 25 | 5 |
| 50 | 10 |
| 100 | 20 |
Gram to Carat chart
The reverse direction for values people often look up.
| Gram (g) | Carat (ct) |
|---|---|
| 0.01 | 0.05 |
| 0.02 | 0.1 |
| 0.05 | 0.25 |
| 0.1 | 0.5 |
| 0.2 | 1 |
| 0.5 | 2.5 |
| 1 | 5 |
| 2 | 10 |
| 5 | 25 |
| 10 | 50 |
| 20 | 100 |
Gem weights in carats
| Stone | Carat (ct) | Gram (g) |
|---|---|---|
| One point, a hundredth of a carat | 0.01 | 0.002 |
| Quarter-carat stone | 0.25 | 0.05 |
| One-carat diamond | 1 | 0.2 |
| Hope Diamond | 45.52 | 9.104 |
| Koh-i-Noor, as cut today | 105.6 | 21.12 |
| Cullinan I (Great Star of Africa) | 530.2 | 106.04 |
| Cullinan rough diamond, found in 1905 | 3,106.75 | 621.35 |
Quick mental estimate
Double the carats and divide by 10: 1.5 ct → 3 ÷ 10 = 0.3 g. Because 1 ct is exactly 0.2 g, this shortcut gives the exact answer.
Use the converter or the charts when the exact figure matters.
The two units
Carat (ct): The metric carat is exactly 200 milligrams and is used worldwide to weigh diamonds and other gemstones. It is unrelated to the karat that measures gold purity.
Gram (g): The gram is one thousandth of a kilogram, the SI base unit of mass. It is used worldwide for food, postage and small quantities of almost anything.
Frequently asked questions
Is a carat the same as a karat?
No. A carat (ct) is a mass of 200 mg used for gemstones. A karat (K or kt) measures gold purity in 24ths: 24K is pure gold and 18K is 75% gold. US usage keeps the two spellings apart; elsewhere carat is often used for both.
What does a diamond's point size mean?
One point is a hundredth of a carat, or 2 mg. A 25-point stone is a quarter carat (0.05 g), and a 75-point stone is three quarters of a carat (0.15 g). Point sizes are mostly used for stones under one carat.
Does carat weight show how big a gemstone looks?
Only roughly. Carat is mass, so two diamonds of the same weight can face up at different sizes depending on how they are cut, and denser gems look smaller for their weight: a 1 ct ruby is smaller than a 1 ct diamond because corundum is denser.
How precise is the result?
The converter uses the exact definitions above with browser floating-point arithmetic and shows up to 12 significant digits. The charts round to four decimal places for reading.
Sources
Last updated:
Page address with these inputs: https://kakao.mobile/tools/carat-to-gram-converter/
Cite or embed this tool
kakaoCalc. (2026, November 8). Carats to Grams Converter (ct to g). https://kakao.mobile/tools/carat-to-gram-converter/
“Carats to Grams Converter (ct to g).” kakaoCalc, 8 Nov. 2026, kakao.mobile/tools/carat-to-gram-converter/.
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