Carat to Gram Converter
Quick answer
1 carat = 0.2 grams = 200 milligrams, and 1 gram = 5 carats. A carat is split into 100 points, so 0.50 ct is 50 points. The gem trade grain is a quarter carat. Use the converter below for ounces, troy ounces and pennyweights.
Exact definitions, no estimation involved. Data verified .
Convert carats, grams and other weight units
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Carat to gram, in one line
The metric carat is exactly 200 milligrams. Divide carats by 5 to get grams, or multiply grams by 5 to get carats. Unlike the size conversions on this site, there is no estimate involved here. It is pure arithmetic, and the converter gives the same answer every time.
Conversion table
| Carats | Grams | Milligrams | Points | Pearl grains | Troy ounces |
|---|---|---|---|---|---|
| 0.01 ct | 0.002 | 2 | 1 | 0.04 | 0.00006 |
| 0.1 ct | 0.020 | 20 | 10 | 0.40 | 0.00064 |
| 0.25 ct | 0.050 | 50 | 25 | 1.00 | 0.00161 |
| 0.5 ct | 0.100 | 100 | 50 | 2.00 | 0.00322 |
| 1 ct | 0.200 | 200 | 100 | 4.00 | 0.00643 |
| 2 ct | 0.400 | 400 | 200 | 8.00 | 0.01286 |
| 5 ct | 1.000 | 1,000 | 500 | 20.00 | 0.03215 |
| 10 ct | 2.000 | 2,000 | 1,000 | 40.00 | 0.06430 |
| 25 ct | 5.000 | 5,000 | 2,500 | 100.00 | 0.16075 |
| 50 ct | 10.000 | 10,000 | 5,000 | 200.00 | 0.32151 |
| 100 ct | 20.000 | 20,000 | 10,000 | 400.00 | 0.64301 |
The units, explained
- Carat
- 200 mg, or 1.0000 ct
- Point
- 2 mg, or 0.010 ct
- Milligram
- 1 mg, or 0.005 ct
- Gram
- 1,000 mg, or 5.0000 ct
- Pearl grain (gem trade)
- 50 mg, or 0.2500 ct
- Grain (troy, apothecary)
- 64.79891 mg, or 0.3240 ct
- Pennyweight
- 1,555.17384 mg, or 7.7759 ct
- Ounce (avoirdupois)
- 28,349.523125 mg, or 141.7476 ct
- Troy ounce
- 31,103.4768 mg, or 155.5174 ct
Carat (ct). The standard unit for gems everywhere. Most scales used by gem dealers read to 0.001 ct or 0.01 ct.
Point (pt). A hundredth of a carat. Small stones in pavé and halos are described in points, for example "1.5 pt melee". Ten 5 pt stones add up to half a carat.
Gram and milligram. Used for rough material, beads, cabochon lots and mounted jewellery. Precious metal is weighed in grams too, so a ring might be described as "4.2 g total weight".
Pearl grain. The traditional pearl unit, a quarter carat. Natural pearls are still sometimes sold by the grain.
Troy grain and pennyweight. Old units still used by some jewellers for metal, especially in the US. One pennyweight (dwt) is 24 troy grains, about 7.7759 ct.
Ounces. An avoirdupois ounce, the everyday kitchen ounce, is about 141.75 ct. A troy ounce, used for gold and silver, is heavier at about 155.52 ct.
Where conversions trip people up
- Grams in a ring listing usually mean the whole ring. A "5 g" ring includes the metal. The stone is often a small fraction of that.
- Total carat weight. "2 ct TW" is the sum of all stones. Our total carat weight calculator helps you split it up.
- Rounding on scales. A scale that reads to 0.01 g can only resolve 0.05 ct. For small stones, a carat scale is far more precise.
- Diamond equivalent weight. Moissanite listed as "1 ct DEW" does not weigh 0.2 g. Its real weight is lower. See moissanite vs diamond size.
Weight tells you how much material you are buying. Size tells you how big it looks. To go from one to the other, use the carat to mm size finder or read what a carat is.
For a 1 ct stone, the converter gives 0.20 g. For a 25 ct parcel of melee, 5.00 g. For a 100 ct lot of rough, 20.00 g. Those three figures cover most everyday checks a buyer or seller needs.
Related questions
How many grams is 1 carat?
Exactly 0.2 grams. The metric carat was defined as 200 milligrams and adopted internationally in the early twentieth century, so the conversion never changes.
How many carats are in a gram?
Exactly 5 carats. So a 2.5 g lot of loose stones weighs 12.5 ct in total.
What is a point in carat weight?
One hundredth of a carat. A 0.25 ct stone is "25 points" and a 0.05 ct melee stone is "5 points". Sellers often write "pt".
How many carats is a troy ounce?
About 155.52 carats. Troy ounces are used for precious metals, not for gems, but it helps when comparing the weight of a stone with the gold around it.
Is a grain the same as a carat?
No. In the pearl and gem trade a grain is a quarter carat (50 mg), so 1 ct = 4 pearl grains. The troy or apothecary grain is a different unit of 64.79891 mg, so 1 ct is about 3.0865 troy grains. Check which grain a listing means.
Why do some listings give weight in grams?
Rough, beads, cabochon lots and large carvings are often sold by the gram. Faceted gems are almost always sold by the carat. Convert to carats before comparing prices.
How do I convert a price per gram to price per carat?
Divide the price per gram by 5. A rough lot at 50 per gram is 10 per carat. The price per carat calculator does it both ways.
Does a carat have anything to do with gold karats?
No. Gem carats measure weight. Gold karats (spelled with a k in US English) measure purity out of 24. The words share a history but not a meaning.
Sources and method
Weight estimates use the colored-stone shape factors published by the International Gem Society and the Dendritics standard formula, and the diamond trade constants and length to width ratio tables published in jewelry trade references (Esslinger, Omni, Octonus). Specific gravity values are cross-checked against the International Gem Society density tables, the USGS Natural Gemstones report and GemSelect.
Every number on this page is generated by the same formula engine as the calculators. Read the full method, constants and limits and the editorial policy. Data last verified 2026-11-04.
Estimates only. This is not an appraisal, grading report or valuation. A calibrated scale or a lab report is the only real weight.