Carat Weight Calculator

Carat weight is a measure of mass, where one carat equals exactly 200 milligrams (0.2 grams). Because removing a stone from its setting to weigh it on a scale is often impractical, gemologists rely on geometric formulas that incorporate millimeter measurements and specific gravity adjustments. For a standard round brilliant cut, the formula multiplies the squared diameter by the depth, multiplied by a standard proportion constant (approximately 0.0061) along with any girdle thickness factor (GTF). Fancy cuts like oval, cushion, princess, and emerald factor in length, width, depth, and shape-specific multipliers to account for pavilion depth percentages and crown heights.

Let us calculate the estimated carat weight of a standard Oval cut diamond set in a ring. Suppose you take careful caliper measurements of the stone: the length is 8.0 mm, the width is 6.0 mm, and the depth is 3.7 mm. Assume standard girdle thickness and waste correction factors where GTF and WCF equal zero. Using the oval formula: Weight = Length (8.0) * Width (6.0) * Depth (3.7) * 0.0062. Multiplying these values together gives 8.0 * 6.0 = 48.0; then 48.0 * 3.7 = 177.6; and finally 177.6 * 0.0062 = 1.10112 carats. Thus, the estimated weight of the oval diamond is approximately 1.10 carats.

To achieve the most accurate carat estimation, always use digital calipers calibrated in millimeters rather than a standard ruler. Measure each dimension at the widest and thickest points while taking care not to scratch the girdle or table of the stone. Keep in mind that calculated carat weights are close approximations; variations in cut proportions, pavilion bulges, or culet sizes can cause slight deviations from actual scale weights.