This “C” is the one that refers to weight, not size. The size of the stone is determined by the cut. The weight is constant due diamond’s own unique specific gravity. The term “carat” is derived from the carob seed, which was an ancient form of exchange and measuring. 1 carat or 1.00 ct. can be broken down into points, which are fractions of a carat. .25 = one quarter carat. .50 = one half carat and so one. The average, well-cut 1.00 ct. round measures approx. 6.5 mm across. Any given stone can be cut wider and shallower or narrower and deeper and still weigh 1 ct. In the first case, the stone will look bigger and in the second, it will look smaller.
With regards to fancy cuts which include anything except round, each shape has it’s own recommended set of proportions. Generally speaking, stones that have length and width will appear “bigger” than the equivalent round. Princess cuts are an exception because most of the weight of those stones is in the bottom portion called the pavilion. A well cut round will always have a larger diameter than the same weight in princess cut.
Yantz Bradbury Associates
P.O. Box 10123
Rockville, Maryland 20850
Office: (301) 335-6687
Serving MD, VA and DC Metro Area