ct
Definition
The metric carat equals 200 milligrams exactly. It is the standard unit for gemstone weight — diamonds, rubies, sapphires and emeralds are sold by the carat. Do not confuse with the purity carat (karat) used for gold (24K = pure gold).
Common uses
- Diamond and gemstone retail and valuation
- Jewellery manufacturing and design
- International gem certification (GIA, IGI)
🌍 Real-world scale
A 1-carat diamond weighs 200 mg and is typically 6.5 mm across. The Hope Diamond is 45.52 carats (9.1 g).
Convert from carats
11 conversionsCarat to Kilogram1 ct = 0.0002 kgCarat to Gram1 ct = 0.2 gCarat to Milligram1 ct = 200 mgCarat to Microgram1 ct = 200,000 µgCarat to Pound1 ct = 0.0004409 lbCarat to Ounce1 ct = 0.007055 ozCarat to Metric Ton1 ct = 2.0000e-7 tCarat to US Ton1 ct = 2.2046e-7 ton (US)Carat to UK Ton1 ct = 1.9684e-7 ton (UK)Carat to Stone1 ct = 3.1495e-5 stCarat to Grain1 ct = 3.08647 gr
Convert to carats
11 conversionsKilogram to Carat1 kg = 5,000 ctGram to Carat1 g = 5 ctMilligram to Carat1 mg = 0.005 ctMicrogram to Carat1 µg = 5.0000e-6 ctPound to Carat1 lb = 2,267.96 ctOunce to Carat1 oz = 141.748 ctMetric Ton to Carat1 t = 5,000,000 ctUS Ton to Carat1 ton (US) = 4,535,923.7 ctUK Ton to Carat1 ton (UK) = 5,080,234.54 ctStone to Carat1 st = 31,751.47 ctGrain to Carat1 gr = 0.324 ct
Tips
- 1 carat = 200 mg = 0.2 g exactly since 1907.
- Carat (gem weight) and karat (gold purity, 24 K = pure) are different words with different meanings.
- A carat is divided into 100 points; a 0.25 ct diamond is called a "25-pointer".
Common mistakes
- Confusing carat (mass) with karat (gold purity).
- Assuming a 2-carat diamond is twice the physical size of a 1-carat — volume scales with cube root of mass.
- Using "karat" on gemstone certificates — international standard is "carat" spelled with a C.
FAQ about the carat
Explore all 12 weight units and their conversions.⚖️ Weight hub →