Natural Gemstones are used in ample in jewellery settings. There are some handy formulas for estimating the weight of gemstones in settings. These formulas could be used where the stones cannot be removed for accurate weighing. The formulas are displayed below for your convenience. These formulas are calculated for well-proportioned stones, however 2% to 6% could be added for bulge factor i.e. extremely steep crown or pavilion angles. Also remember that the resulting weights of these formulas are estimated only, accuracy could be achieved only after correct estimation of bulge aspects.

Note:
All weights are specified in carats. 

All measurements are given millimeters (mm). 3. An asterisk (*) indicates multiplication.

A Slash (/) specifies division.5. 

S.G. points to specific gravity (see individual stone descriptions for values or the url).

Formulas:
1. Used for round faceted stones:
weight = average diameter * average diameter * total depth * S.G. * .0018

2. Used for oval faceted stones:
average diameter = (length + width) / 2
weight = average diameter * average diameter * total depth * S.G. * .0020

3. Used for rectangular faceted stones:
weight = length * width * total depth * S.G. * .0026

4. Used for square or emerald cut faceted stones:
weight = length * width * total depth * S.G. * .0025

5. Used for pear shaped or heart shaped faceted stones:
weight = length * width * total depth * S.G. * .0018