Diamond carat: weight, size and practical equivalences
The carat is the unit of mass used to weigh precious stones. 1 carat (ct) = 0.20 grams. For a round brilliant diamond of ideal proportions, there is an approximate correspondence between carat weight and diameter in millimeters, allowing jewelers to quickly estimate the visual size of a stone.
Key equivalences for a round brilliant diamond of excellent proportions: 0.25ct ≈ 4.0mm, 0.50ct ≈ 5.0mm, 0.75ct ≈ 5.8mm, 1.00ct ≈ 6.5mm, 1.50ct ≈ 7.3mm, 2.00ct ≈ 8.1mm, 3.00ct ≈ 9.3mm. These values vary slightly depending on the depth and proportions of each diamond.
For non-round shapes (emerald, princess, oval, pear), the weight/surface ratio is different: an emerald-cut 1.00ct appears smaller than a 1.00ct round because it has greater depth. Our catalog systematically displays real dimensions in millimeters for each stone, allowing precise evaluation regardless of carat weight.