The C's: Carat Weight
Diamond weight is expressed in carats (one carat is equal to 200 milligrams). Carats are divided into 100 points so a 0.78 ct diamond is called a 78 pointer.
Cut influences Carat Weight
The majority of poor performance diamonds were purchased with carat weight and size being the most important factor in the decision to buy. Diamonds that weigh the same may not have the same vertical spread, depending on how they were cut. Those cut too shallow or too deep will look small for their weight and/or have poor light performance.
The goal of most cutters is to maximize carat weight from pieces of rough. This means many diamonds are cut too shallow or deep. A diamond’s grading report lists its measurements in millimeters. The first two numbers are min and max spread; be sure the diamond has appropriate spread for carat weight. Once this is correct, you then need to evaluate the critical angles necessary for light performance.
Diamonds cut for the highest level of performance have critical angles and precision-cutting which make the diamond explode with edge-to-edge brightness. Such superior light performance diamonds appear larger than diamonds of normal cut quality.
Only a fraction of the world’s diamonds have such cut quality; they are rare enough that most people have never even seen one. Bright jewelry store lighting makes all diamonds look good. Diamonds with the most elite level of light performance and precision are seen in the American Gem Society ASET® scope. Such superior performance diamonds are simply just not available to most sellers.
Diamond prices increase exponentially between the following ranges: .50ct, .70ct, .90ct, 1.00ct, 1.50ct, 2.00ct and every half carat increase in weight from 2.00ct and onward. Basically larger diamonds cost disproportionately more as pieces of rough material are increasingly rare with size.