As a general rule, a cut gemstone will reduce the mass (in carats) by about 50%.
[1] Among the several techniques used to work with gemstones are sawing, grinding, sanding, lapping, polishing, grilling, and tumbling.
The diamond cut planning stage is a complex process that requires the cutter to work with unique rough stones.
Very often, the location of the inclusions in a rough stone will determine the type of shape to which a diamond may be cut.
For economic reasons, most diamonds are cut to retain weight instead of maximizing brilliance.