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Convert carats (ct) to grams (g) instantly with our free gemstone weight calculator. Accurate carat to gram conversion for diamonds, rubies, sapphires, and all precious stones.
1 carat (ct) = 0.2 grams (g)
Grams = Carats x 0.2 | Carats = Grams / 0.2
| Carats (ct) | Grams (g) | Real-World Context |
|---|---|---|
| 0.1 | 0.02 | Small accent diamond |
| 0.25 | 0.05 | Quarter-carat engagement stone |
| 0.5 | 0.10 | Half-carat solitaire |
| 0.75 | 0.15 | Three-quarter carat ring |
| 1 | 0.20 | Classic 1-carat diamond |
| 1.5 | 0.30 | Popular engagement ring size |
| 2 | 0.40 | Premium solitaire |
| 3 | 0.60 | Large statement diamond |
| 4 | 0.80 | High-end collector stone |
| 5 | 1.00 | Rare investment-grade gem |
| 10 | 2.00 | Museum-quality gemstone |
| 25 | 5.00 | Exceptional specimen |
| 50 | 10.00 | Major auction piece |
| 100 | 20.00 | World-record territory |
| 200 | 40.00 | Historic gemstone weight |
| 500 | 100.00 | Large uncut rough stones |
| 1000 | 200.00 | Major rough diamond finds |
The metric carat (symbol: ct) is the standard unit of mass used to measure gemstones and pearls in the international jewelry trade. One carat is defined as exactly 200 milligrams (0.2 grams or 0.00705 ounces). The metric carat was formally adopted in 1907 at the Fourth General Conference on Weights and Measures, replacing a patchwork of regional carat definitions that varied from country to country.
The word "carat" traces its origins to the Greek word keration, referring to the seed of the carob tree (Ceratonia siliqua). Ancient gem traders used carob seeds as counterweights on balance scales because they believed each seed had a remarkably consistent mass of roughly 200 mg. Modern research has shown carob seeds actually vary more than once thought, but the convention stuck and eventually became formalized in the metric system.
It is important to distinguish carat from karat. Carat measures mass (weight) and applies to gemstones. Karat (abbreviated K or kt) measures the purity of gold alloys on a scale from 1 to 24, where 24 karat means pure gold. A "2-carat 18-karat gold ring" has a 0.4-gram diamond set in 75%-pure gold. The gram (symbol: g) is the base metric unit of mass equal to one-thousandth of a kilogram, making the carats-to-grams conversion a simple multiplication by 0.2.
grams = carats x 0.2
Equivalently: grams = carats / 5
Reverse: carats = grams / 0.2 (or grams x 5)
Question: How many grams does a 1.5 ct diamond weigh?
Question: Convert 3 carats to grams.
Question: What does the famous Hope Diamond weigh in grams?
Since 1 carat = 0.2 g, simply divide the carat value by 5 to get grams. For example, 10 ct / 5 = 2 g. This works because 0.2 is the same as 1/5. For the reverse, multiply grams by 5 to get carats.
100 points = 1 carat. Jewelers often quote small diamonds in points.
| Points | Carats (ct) | Grams (g) |
|---|---|---|
| 5 | 0.05 | 0.0100 |
| 10 | 0.10 | 0.0200 |
| 15 | 0.15 | 0.0300 |
| 25 | 0.25 | 0.0500 |
| 33 | 0.33 | 0.0660 |
| 50 | 0.50 | 0.1000 |
| 75 | 0.75 | 0.1500 |
| 100 | 1.00 | 0.2000 |
Putting carat-to-gram conversion in perspective with famous stones.
| Gemstone | Carats (ct) | Grams (g) |
|---|---|---|
| Hope Diamond | 45.52 | 9.10 |
| Koh-i-Noor Diamond | 105.6 | 21.12 |
| Cullinan I (Great Star of Africa) | 530.2 | 106.04 |
| Star of India (Sapphire) | 563.35 | 112.67 |
| Bahia Emerald | 840 | 168.00 |
| Cullinan Diamond (rough) | 3106.75 | 621.35 |
Typical carat weights for engagement diamonds and their gram equivalents.
| Description | Carats (ct) | Grams (g) | Milligrams (mg) |
|---|---|---|---|
| Petite solitaire | 0.3 | 0.06 | 60 |
| Classic half-carat | 0.5 | 0.10 | 100 |
| Popular choice | 0.75 | 0.15 | 150 |
| One carat standard | 1 | 0.20 | 200 |
| Premium choice | 1.5 | 0.30 | 300 |
| Luxury solitaire | 2 | 0.40 | 400 |
| High-end statement | 3 | 0.60 | 600 |
| Rare collector piece | 5 | 1.00 | 1000 |
Understanding carat weight in grams helps buyers compare stone sizes across different jewelers and online listings, ensuring you know exactly how much gemstone you are paying for.
Gemologists routinely convert between carats and grams when working with laboratory balances calibrated in metric units, ensuring precise certification of gemstone weights.
Insurance companies and customs agencies often require gem weights in metric grams for documentation, import/export declarations, and accurate valuation of jewelry.
The global gemstone market trades across borders, and converting carats to grams bridges the gap between jewelry-industry terminology and the metric system used in shipping and logistics.
Carat (ct) measures gem weight; karat (K/kt) measures gold purity. Mixing them up is the most common mistake in jewelry weight conversations.
Two 1-carat gemstones can look very different in size depending on the stone's density and cut. A 1-ct sapphire appears smaller than a 1-ct diamond because sapphire is denser.
Multiply grams by 5 to get carats, or divide carats by 5 to get grams. This is the fastest mental math approach since 1/0.2 = 5.
Multi-stone jewelry often lists the total carat weight of all stones combined, not the weight of the center stone alone. Always clarify whether the weight is for a single stone or the entire piece.
Diamonds under 1 carat are commonly quoted in points (1 point = 0.01 ct = 0.002 g). A "75-point diamond" is 0.75 ct or 0.15 g.
One carat equals exactly 0.2 grams or 200 milligrams. This is the internationally standardized metric carat adopted in 1907.
No. Carat (ct) measures gemstone weight, while karat (K or kt) measures gold purity. A 24-karat gold item is pure gold; a 1-carat diamond weighs 0.2 grams. They are completely different measurements despite the similar spelling.
Carats provide a standardized, precise measurement for small, valuable gemstones. The carat system has been used for centuries in the jewelry trade and became internationally standardized in 1907 at the Fourth General Conference on Weights and Measures.
A 1-carat diamond weighs exactly 0.2 grams or 200 milligrams. This weight is the same for any gemstone because the carat is a unit of mass, not size.
The word "carat" derives from the carob seed (Greek: keration), which was used historically as a reference weight in gem trading because of its relatively uniform mass of about 200 mg. The modern metric carat was standardized in 1907.
Carats are the universal standard for measuring all gemstones and pearls, including diamonds, rubies, sapphires, emeralds, and other precious and semi-precious stones. The unit applies to any gemstone regardless of type.
To convert grams to carats, divide the gram value by 0.2 (or multiply by 5). For example, 1 gram equals 5 carats, and 0.5 grams equals 2.5 carats.
A point is one-hundredth of a carat (0.01 ct). A 50-point diamond weighs 0.5 carats (0.1 grams), and a 25-point diamond weighs 0.25 carats (0.05 grams). Jewelers use points for diamonds under one carat.
This calculator is provided for informational and educational purposes only. While we strive for accuracy, always verify critical measurements with certified gemological equipment. UnitTables is not responsible for decisions made based on these calculations.