Carat Weight Estimator

Jewelers and gemologists estimate carat weight from dimensions whenever a stone is already mounted and cannot be pulled for a scale reading -- the standard method multiplies Length, Width, and Depth (all measured in millimeters, table to culet for depth) by a shape-specific correction factor, then scales the result by how dense the material is relative to diamond, since a round brilliant, an emerald cut, and a marquise of identical bounding-box dimensions do not contain the same volume of material. This calculator applies that same length-times-width-times-depth method. The published shape factors are all calibrated for diamond, so Specific Gravity enters as a ratio against diamond's own 3.52: a ruby or sapphire at about 4.0 comes out roughly 13% heavier than a diamond of identical dimensions, and an emerald at 2.72 roughly 23% lighter. Entering the wrong material's specific gravity is one of the most common sources of error in a caliper estimate.

Shape sets the correction factor: a Round Brilliant uses roughly 0.0061, while an Emerald/Rectangle cut uses a larger factor (about 0.0080) because more of its bounding box is actually filled with stone. Depth % and L:W Ratio are reported alongside the weight estimate because they are standard proportion checks jewelers use to sanity-check a cut, not because they feed back into the weight formula. What this calculator cannot do is replace a scale: caliper-based estimates assume an idealized cut proportion for the chosen shape, so a stone cut unusually deep or shallow, or one with a non-standard girdle, will estimate off from its true weight even with perfectly accurate measurements -- which is what the Girdle Thickness Adjustment is for, since a thick or very thick girdle can add 3 to 12% to a stone's weight without changing its face-up size at all.