Estimating Weight of Gemstones
You cannot weigh a gem in a setting and it is rarely worth removing. Instead, you can get a close approximation of the weight by the gem’s volume.
In order to use these formulas, your measurements must be extremely accurate. Careful observation is also important. All these weights are adjusted by the stones proportions and it takes a trained eye to make those judgments.
Round faceted stones:
Emerald cut faceted stones:
Square cut faceted stones:
Marquise cut stones, (navette):
Pear cut stones:
Square cushions: (average corner meas.& belly meas. for diameter)
Rectangular Cushions: (average L & W for diameter)
Square step cut stones: (average both meas. for diameter)
Rectangular step cut stones:
Cabochon cut stones: