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Gemstone Carat to MM Calculator

Gemstone Carat to MM

Convert gemstone weight in carats to approximate dimensions in millimeters based on gem type, cut shape, and specific gravity.

Formula

Mass (g) = Carats x 0.2; Volume (mm3) = Mass / Specific Gravity x 1000; Diameter = cube root of (Volume / (Depth Ratio x Width Ratio x pi/4))

Frequently Asked Questions

How big is a 1 carat diamond?
A 1 carat round brilliant diamond is approximately 6.5mm in diameter. However, the exact dimensions depend on the cut proportions and depth. Well-cut diamonds may appear larger face-up.
Does gemstone type affect size for the same carat weight?
Yes, because different gems have different densities (specific gravity). A 1 carat emerald (SG 2.72) is physically larger than a 1 carat ruby (SG 4.03) because emerald is less dense.
What is a carat?
A carat is a unit of weight equal to 200 milligrams (0.2 grams). It is the standard measure for gemstones. It should not be confused with karat, which measures gold purity.

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