Diamond Weight Calculator

Diamond weight is officially measured in carats, with one carat equal to 0.2 gram. A precision gem scale is the authoritative way to weigh a loose stone, yet many diamonds are already mounted or described only by dimensions. A dimensional estimate converts the stone's approximate volume into carats and can help with preliminary identification, inventory work, insurance discussions, or comparisons between listings. This calculator multiplies length, width, and depth in millimeters, then applies a coefficient selected for the outline. The coefficient combines diamond's density with an approximation of the cut shape. Round diamonds use 0.0061, ovals use 0.0062, rectangular emerald and princess cuts use 0.0080, marquise cuts use 0.00565, and pear shapes use 0.00615. These are practical trade estimates rather than exact geometric constants because faceted stones do not fill a simple rectangular volume. Measure length at the longest girdle dimension, width perpendicular to it, and depth from table to culet. For a round stone, length and width can be the minimum and maximum diameter; multiplying both has the same effect as squaring their geometric mean. Use a gem gauge or careful digital caliper and record at least two decimal places when possible. Never apply enough pressure to chip a girdle, and account for any setting parts that obstruct the measurement. Shape matters because different outlines and facet arrangements occupy different fractions of the bounding dimensions. An emerald-cut diamond resembles a truncated rectangular solid more closely than a marquise, so its coefficient is larger. Even within one named shape, crown angle, pavilion depth, girdle thickness, bulge, and culet can change actual mass. Antique cuts and highly modified fancy shapes may differ substantially from modern coefficient assumptions. The result should be treated as an estimate, not a grading statement. Measurement error affects all three dimensions, and a small error can be meaningful on a valuable stone. The calculator also assumes the material is diamond; simulants with different densities will not follow these coefficients. Obtain an unmounted scale weight and a report from a qualified gemologist or recognized laboratory when an exact carat value affects price, insurance coverage, or legal documentation.