A gemstone, unlike a diamond, has no defined proportions. Hence, it is available in proportions that are largely determined by the cutter or manufacturer.
The basic idea is to maximize the yield (the weight of the stone, after the stone is cut and polished). And because there is no set of proportions that the manufacturer has to follow, he uses his knowledge to bring out the best possible outcome.
A set of proportions which is known as ‘machine cut’ is the nearest a manufacturer can achieve to the ideal cut.
A Breakdown of Gemstone Proportions
