Instantly Convert Grams ↔ Carats — Both Directions
Convert grams to carats (g → ct) or carats to grams (ct → g) instantly. Get the exact conversion with formula breakdown, reference table, and real-world gemstone examples — all free, no sign-up needed.
The gram is the standard SI unit of mass used in everyday life, while the carat is the specialist unit used to weigh gemstones, diamonds, and precious stones worldwide. Our free grams to carats converter handles both directions instantly using the exact conversion factor of 1 gram = 5 carats — the internationally defined metric carat standard.
The gram (g) is a unit of mass in the International System of Units (SI), equal to one-thousandth of a kilogram. It is the standard everyday unit for measuring the weight of food, medicine, and small objects worldwide. In the context of gemstones, grams are used for larger stones or bulk gem parcels, while individual gemstones are almost always described by their weight in carats.
The metric carat (ct) is the unit of mass used universally for weighing gemstones, diamonds, pearls, and other precious stones. Since 1907, 1 metric carat = exactly 0.2 grams — a definition adopted internationally and still in use today. The word "carat" comes from the carob seed (Ceratonia siliqua), which was historically used as a counterweight in gemstone trading across the ancient Middle East and Mediterranean.
The exact conversion factor is 1 gram = 5 carats and 1 carat = 0.2 grams. This is a perfectly clean, exact relationship with no rounding required. The formula for grams to carats is: carats = grams × 5. The reverse is equally simple: grams = carats ÷ 5. All conversions on this page use these exact values as defined by international agreement since 1907.
Choose a direction, enter your value, and get an instant conversion
The grams to carats conversion is one of the simplest unit conversions in the metric system. Since 1907, the metric carat has been defined as exactly 0.2 grams — making the relationship between grams and carats a perfectly clean factor of 5. There is no rounding, no approximation, and no ambiguity. Both formulas below are mathematically exact by international definition.
The table below lists commonly needed gram to carat conversions. All values use the exact factor of 1 g = 5 ct. For carats to grams, refer to the second table below or use the direction toggle on the converter above.
| Grams (g) | Carats (ct) | Milligrams (mg) | Ounces (oz) | Common Context |
|---|---|---|---|---|
| 0.01 g | 0.05 ct | 10 mg | 0.000353 oz | Very small diamond chip |
| 0.04 g | 0.2 ct | 40 mg | 0.00141 oz | Small diamond — 0.2 ct solitaire |
| 0.1 g | 0.5 ct | 100 mg | 0.00353 oz | Half-carat diamond |
| 0.2 g | 1 ct | 200 mg | 0.00706 oz | 1-carat diamond (classic solitaire) |
| 0.4 g | 2 ct | 400 mg | 0.01411 oz | 2-carat diamond — luxury ring |
| 0.6 g | 3 ct | 600 mg | 0.02116 oz | 3-carat diamond — premium stone |
| 1 g | 5 ct | 1,000 mg | 0.03527 oz | 5-carat diamond — exceptional stone |
| 2 g | 10 ct | 2,000 mg | 0.07055 oz | 10-carat gem — museum quality |
| 5 g | 25 ct | 5,000 mg | 0.17637 oz | Large gem parcel / coloured stones |
| 10 g | 50 ct | 10,000 mg | 0.35274 oz | Gem parcel weight |
| 20 g | 100 ct | 20,000 mg | 0.70548 oz | Large gem / rough crystal |
| 50 g | 250 ct | 50,000 mg | 1.7637 oz | Bulk gem parcel |
| 100 g | 500 ct | 100,000 mg | 3.5274 oz | Wholesale gem parcel |
| 200 g | 1,000 ct | 200,000 mg | 7.0548 oz | Large wholesale gem lot |
| 1,000 g (1 kg) | 5,000 ct | 1,000,000 mg | 35.274 oz | 1 kilogram of gemstones |
Need to convert the other way? The table below shows common carat values converted to grams. All values use the exact factor of 1 ct = 0.2 g. These are the most common carat weights encountered in jewellery, diamond grading, and gemstone trading in 2026.
| Carats (ct) | Grams (g) | Milligrams (mg) | Common Context |
|---|---|---|---|
| 0.1 ct | 0.02 g | 20 mg | Melee diamond (accent stone) |
| 0.25 ct | 0.05 g | 50 mg | Quarter-carat — small solitaire |
| 0.5 ct | 0.1 g | 100 mg | Half-carat diamond ring |
| 0.75 ct | 0.15 g | 150 mg | Three-quarter carat stone |
| 1 ct | 0.2 g | 200 mg | Classic 1-carat solitaire diamond |
| 1.5 ct | 0.3 g | 300 mg | 1.5-carat engagement ring |
| 2 ct | 0.4 g | 400 mg | Luxury 2-carat diamond ring |
| 3 ct | 0.6 g | 600 mg | Premium 3-carat stone |
| 5 ct | 1.0 g | 1,000 mg | Exceptional 5-carat diamond |
| 10 ct | 2.0 g | 2,000 mg | Very rare 10-carat gemstone |
| 25 ct | 5.0 g | 5,000 mg | Famous named diamonds (e.g. Sancy) |
| 100 ct | 20.0 g | 20,000 mg | Extraordinary large stone |
| 500 ct | 100.0 g | 100,000 mg | Rough gem crystal / bulk parcel |
The gram to carat conversion is essential in the gemstone, jewellery, and precious metals industries worldwide. Here are the most common and practical situations where converting grams to carats — or carats to grams — is needed in 2026.
All diamonds and precious gemstones are bought and sold by weight in carats worldwide. Dealers buying rough stones weighed in grams must convert to carats for pricing and grading. A rough diamond weighing 1 gram = 5 carats — and at typical market prices, that single gram of rough diamond can be worth tens of thousands of dollars depending on quality and clarity.
Jewellers sourcing gemstones receive price lists in carats (ct) but may weigh stones on standard gram scales. Converting between grams and carats is a daily task in any jewellery workshop. A 0.5 ct diamond = 0.1 g, while a standard 1 ct solitaire = 0.2 g. Understanding this conversion is essential for accurate costing, inventory management, and client quotations.
Certified gemological laboratories (GIA, IGI, HRD) report all gemstone weights in carats to four decimal places (e.g. 1.0234 ct). When laboratory equipment reports mass in grams or milligrams, technicians must convert to carats for grading reports. The GIA defines gem quality standards that are used globally — their reports list carat weight as the primary mass unit for all certified stones.
International gem and jewellery trade often requires customs declarations in both grams (for regulatory purposes) and carats (for valuation). Importers and exporters regularly convert between the two units for documentation. For example, a parcel declared as 50 grams of diamonds is equivalent to 250 carats — the carat weight being the key figure for calculating customs duty and insurance value.
Students studying gemology, jewellery design, or precious stone valuation must master the grams to carats conversion from day one. Courses at institutions like the Gemological Institute of America (GIA) and the Gemmological Association of Great Britain (Gem-A) teach this conversion as fundamental knowledge. The relationship 1 g = 5 ct is one of the first facts every gemology student memorises.
Online gem trading platforms list stones in carats, while buyers accustomed to metric weights may think in grams. Platforms like Etsy, RapNet, and specialist gem wholesalers display carat weights for all stones. A buyer comparing a 2 ct ruby (0.4 g) to a 5 ct emerald (1 g) needs to quickly convert between the two systems to understand the actual physical size and weight of each stone. For related weight conversions, also see BTU to Joules for energy unit conversions.
The GIA is the world's foremost authority on diamonds, coloured stones, and pearls. Their grading standards, carat weight definitions, and the 4Cs framework are the global industry benchmark used by jewellers and gem laboratories worldwide.
Visit GIA →The International Bureau of Weights and Measures (BIPM) maintains the official definition of the kilogram and gram as SI base units. Their resources explain how the gram fits within the international metric system adopted worldwide.
Visit BIPM →Need to convert other units? ConcreteMetric offers accurate, mobile-friendly converters for weight, length, area, energy, pressure, time, and temperature — all free with no sign-up, updated for 2026.
Browse All Converters →