Estimating Weights of Gemstones in Jewelry Settings

Here are some useful formulas for estimating the weight of stones in settings, where the stones cannot be removed for accurate weighing. All weights are given in carats, and all measurements in millimeters. Dimensions should be measured as accurately as possible using a precision gauge (such as the Leveridge gauge displayed here). An asterisk (*) indicates multiplication; slash (/) indicates division. S.G. stands for specific gravity (see individual stone descriptions for values). These formulas are calculated for well proportioned stones; add 2% to 6% for bulge factor, i.e., excessively steep crown or pavilion angles. The resulting weights are approximate estimates only, and it will take a bit of practice at estimating bulge factors to improve accuracy.

For round faceted stones:

weight = average diameter * average diameter * total depth * S.G. * .0018

For oval faceted stones:

average diameter = (length + width) / 2

weight = average diameter * average diameter * total depth * S.G. * .0020

For rectangular faceted stones:

weight = length * width * total depth * S.G. * .0026

For square or emerald cut faceted stones:

weight = length * width * total depth * S.G. * .0025

For pear shaped or heart shaped faceted stones:

weight = length * width * total depth * S.G. * .0018

[Back to Gemology Pages]