mm to carat conversion

Gemstone weight estimation relies on multiplying the physical volume of the stone by a specific gravity factor unique to the mineral type (most commonly diamond, which has a density of approximately 3.52 g/cm³), adjusted for the geometry of the cut. For a round brilliant cut, the formula is Weight = Diameter² × Depth × 0.0061 × (GTF + 1), where GTF represents the Girdle Thickness Factor. For fancy shapes like oval, princess, or emerald cuts, the equation incorporates length, width, depth, and an additional Waist Correction Factor (WCF) to account for varying pavilion angles and symmetry.

Let us calculate the estimated carat weight for a round brilliant diamond with a measured diameter of 6 mm and a depth of 3.7 mm, assuming a standard girdle thickness factor (GTF) of 0. First, square the diameter: 6 × 6 = 36. Next, multiply by the depth: 36 × 3.7 = 133.2. Finally, multiply this result by the round cut constant of 0.0061: 133.2 × 0.0061 = 0.81252 carats. Thus, the estimated weight of the stone is approximately 0.81 carats.

Always use a digital caliper calibrated in millimeters to measure your gemstone for the highest possible accuracy, as even a tenth of a millimeter discrepancy can noticeably alter the estimated carat weight. Keep in mind that these calculations provide estimations rather than certified weights, because variations in pavilion depth, crown angles, and symmetry can cause two stones with identical table dimensions to weigh differently.