Carat (ct)
The metric carat (ct) is exactly 200 mg. It measures gemstone mass; the karat (K) for gold purity is a different thing.
Symbol: ct
Quantity: mass (commonly called weight)
SI relation: 1 ct = 0.0002 kg (exact)
Derivation: 1 ct = 200 mg (metric carat, exact)
Exact: yes, by definition
Typical uses
- Diamonds and gemstones
- Pearls (sometimes in grains)
- Not to be confused with gold karats (purity)
Convert carats to other units
| Conversion | 1 ct equals | Reverse |
|---|---|---|
| carat to kilogram | 0.0002 kg | kilogram to carat |
| carat to gram | 0.2 g | gram to carat |
| carat to milligram | 200 mg | milligram to carat |
| carat to pound | 0.0004409245244 lb | pound to carat |
| carat to ounce | 0.00705479239 oz | ounce to carat |
| carat to microgram | 200000 µg | microgram to carat |
| carat to metric ton | 2 × 10⁻⁷ t | metric ton to carat |
| carat to stone | 0.00003149460888 st | stone to carat |
| carat to short ton | 2.204622622 × 10⁻⁷ ton (US) | short ton to carat |
| carat to troy ounce | 0.006430149314 oz t | troy ounce to carat |
| carat to long ton | 1.968413055 × 10⁻⁷ ton (UK) | long ton to carat |
| carat to grain | 3.086471671 gr | grain to carat |
Open the Weight and Mass Converter to convert any value between all units.
Sources
- Guide for the Use of the International System of Units (SI), NIST Special Publication 811, 2008 Edition, National Institute of Standards and Technology , Appendix B.8, "carat, metric".
Last reviewed: . Factors are stored exactly and computed with 50-digit decimal arithmetic. See how we verify conversion factors.
Cite this page
APA
Scientific Converters. (2026, October 15). Carat (ct). Retrieved October 17, 2026, from https://scientificconverters.com/units/carat/
IEEE
Scientific Converters, "Carat (ct)," scientificconverters.com. Accessed: Oct. 17, 2026. [Online]. Available: https://scientificconverters.com/units/carat/