Convert gemstone diameter in millimeters to carat weight.
Stone Size
Estimated Weight
Approx Weight1.02ct
Assumes Round (Brilliant) cut with Ideal proportions. "Spready" or "Deep" stones will vary.
Overview
Gemstone carat weight can be estimated from diameter measurements. Different gem types have different densities. Round brilliant cut has standard mm-to-carat ratios.
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Pro Tips
Measure at widest point of stone.
Round diamonds: 6.5mm ≈ 1 carat.
Different cuts have different mm/carat ratios.
Depth percentage affects weight calculation.
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Fun Facts
"1 carat round diamond ≈ 6.4-6.5mm diameter."
"2 carat round diamond ≈ 8.1-8.2mm diameter."
"Ruby/sapphire denser than diamond (more carats per mm)."
"Moissanite less dense than diamond."
Formula: Carat ≈ (Diameter³ × Specific Gravity) / Constant
