Carat Weight
Convert carats to grams and grams to carats instantly. Free online carat weight converter for diamonds gemstones and pearls with bidirectional conversion and weight charts.
About This Calculator
The Carat Weight Calculator lets you quickly convert between carats, grams, and milligrams for diamonds, gemstones, and pearls. Jewelers, gemologists, jewelry buyers, and enthusiasts use this tool to easily switch between the standard carat unit used in the gemstone trade and the metric system units used in everyday contexts. Whether you are evaluating a diamond purchase, comparing gemstone sizes, or working with pearl weights, this bidirectional converter gives you instant accurate results.
The conversion is based on the internationally standardized definition where 1 carat equals exactly 0.2 grams or 200 milligrams. This standard was adopted at the 1907 General Conference on Weights and Measures and is recognized worldwide by the diamond and gemstone industry, including the Gemological Institute of America (GIA), International Gemological Institute (IGI), and all major diamond exchanges in India, the United States, Belgium, and Israel. To convert carats to grams, multiply the carat weight by 0.2; to convert grams to carats, divide by 0.2. Our calculator handles both directions instantly with a breakdown displayed in a chart.
Regional Notes
India: The Indian gemstone and jewellery market predominantly uses carats for diamond trading, especially in Mumbai's Bharat Diamond Bourse and Surat's diamond cutting and polishing industry. The Bureau of Indian Standards recognises the carat as a legal unit for precious stones.
United States: The Federal Trade Commission (FTC) requires diamond weight to be stated in carats with accuracy to at least the third decimal place. US jewellers commonly list both carat weight and gram weight on certification documents from GIA and AGS laboratories.
United Kingdom: The UK National Measurement Office regulates carat weight under the Weights and Measures Act, with the carat defined as 0.2 grams exactly. The London Diamond Bourse and the British Academy of Jewellery use the same international standard.
Frequently Asked Questions
How many grams are in one carat?
One carat equals exactly 0.2 grams or 200 milligrams. This standard was adopted internationally in 1907 and is used worldwide for weighing diamonds, gemstones, and pearls.
How do I convert carats to grams?
To convert carats to grams, multiply the carat weight by 0.2. For example, 5 carats × 0.2 = 1 gram, and 0.5 carats × 0.2 = 0.1 grams. Our carat weight calculator does this instantly.
How do I convert grams to carats?
To convert grams to carats, divide the weight in grams by 0.2. For example, 1 gram ÷ 0.2 = 5 carats, and 0.5 grams ÷ 0.2 = 2.5 carats. Our converter handles both directions.
How many milligrams are in a carat?
One carat equals 200 milligrams. Since 1 gram = 1000 milligrams and 1 carat = 0.2 grams, the conversion is 1 carat × 0.2 g/ct × 1000 mg/g = 200 milligrams.
What is the difference between carat and karat?
Carat (ct) is a unit of mass used for gemstones and pearls equal to 0.2 grams. Karat (K or kt) measures gold purity, where 24 karat is pure gold. They are completely different units despite the similar spelling.
How much does a 1 carat diamond weigh in grams?
A 1 carat diamond weighs exactly 0.2 grams or 200 milligrams. However, carat weight does not directly correspond to physical size — a 1 carat round diamond is approximately 6.5 mm in diameter, but this varies by cut and shape.
Is carat weight the same as diamond size?
No, carat weight measures mass not physical dimensions. Two diamonds of the same carat weight can appear different sizes depending on their cut, shape, and proportions. A well-cut diamond may appear larger than its carat weight suggests.