Carat Weight Converter
Convert between carats, grams, milligrams, ounces troy, and points. Calculate price per carat instantly.
Converter
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Quick Presets
Reference: 1 carat = 0.2 g = 200 mg = 100 points = 0.00643 oz troy
How to Use
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1
Enter weight value
Type the gemstone weight you want to convert into any of the five unit fields (carat, gram, milligram, troy ounce, or point). All other fields update instantly.
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2
Read converted values
All five weight units are calculated bidirectionally in real time. The conversion uses the metric carat standard: 1 ct = 0.2 g = 200 mg = 100 points = 0.00643 oz troy.
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3
Calculate total price (optional)
Enter a price-per-carat value in the optional pricing field to see the total gemstone price based on the current carat weight.
FAQ
What is the difference between carat and karat?
Carat (ct) measures gemstone weight — one metric carat equals 0.2 grams. Karat (K or kt) measures gold purity on a scale of 24 — 24K is pure gold, 18K is 75% gold. Despite sounding identical, they refer to completely different properties in different branches of the jewelry trade.
Why is one carat exactly 0.2 grams?
The metric carat was standardized at the Fourth General Conference on Weights and Measures in 1907 at exactly 200 milligrams (0.2 grams). Before that, the carat varied by region — derived from the carob seed (Ceratonia siliqua), which ancient gem traders believed had uniform weight. The 200 mg standard was a compromise that closely matched the most widely used historical values.
What is the point system in gemstone weight?
A point is one hundredth of a carat, so 100 points equal 1 carat. Jewelers use points for precision with small stones — a 0.25-carat diamond is called a '25-pointer.' This system avoids confusing decimal fractions and is standard in diamond grading reports from GIA and other labs.
Does carat weight determine gemstone size?
No — carat measures weight, not dimensions. Two gems of the same carat weight can look very different in size because of density (specific gravity). A 1-carat opal (SG 2.1) is visually larger than a 1-carat ruby (SG 4.0) because the opal is less dense and spreads over a bigger area for the same mass.
Which gemstone is the most expensive per carat?
Top-quality red diamonds, blue diamonds, and Burmese rubies consistently set per-carat price records, sometimes exceeding $1 million per carat at auction. Among colored stones, Kashmir sapphires, Colombian emeralds, and Paraiba tourmalines regularly command $50,000–$200,000 per carat for exceptional specimens.