Diamond Carat
The unit of weight used for diamonds is the metric carat (0.200 grams). The word "carat" comes from the carob seeds (inedible seeds of the locust tree) which were used anciently as standard weight measurement. Weight is the most objective measurement of the 4 Cs because loose diamonds can be weighing directly on scales. A full carat is referred to as 1.00 ct., or 100 points. One-half carat is written .50 ct., or referred to as 50 points. One-quarter carat would thus be .25 ct., or 25 points, and so on. Every aspect of a diamond is measured in minute details. For example, it would require nearly one hundred and forty-two full one carat diamonds just to equal one ounce. The worlds largest gem-quality rough diamond ever discovered (1905) was the Cullinan from South Africa which weighing over 3,100 carats. This diamonds was cut into nine smaller diamonds, the largest of which was a 530.20 ct., pear-shaped diamond known as the "Great Star of Africa." Diamond mining is an enormous undertaking which yields very little weight based on the material collected. It takes about 250 tons of mined material to yield a single one-carat diamond.
Because the carat measurement is a weight measurement, appraisers measuring mounted diamonds must use weight estimation formulas to determine the approximate carat weight of the mounted stone. These formulas can yield fairly accurate estimations usually within 10 percent. Nevertheless, consumers must understand weight estimations taken diamonds in their mounting are still estimations. An analogy would be if a health expert were to measure your height, width, and girth to determine your body weight without using a scale.
Carat weight is the single biggest factor in diamond pricing, but it's important to understand the difference between a single stone's carat weight and a ring's carat total weight. Carat weight pricing rises exponentially. For example an SI1 H (see clarity and color for explanation of these references) round brilliant diamond weighing .25 ct. may (prices are simply for example purposes and may not accurately reflect the price of these stones) cost 1500 per carat. Which means at .25 ct. this diamond would sell for $375 (1500 x .25 = $375). A .50 ct., round brilliant diamond on the other hand, of the same quality may sell for $3800 per carat, or $1900 for this particular .50 ct. diamond. Then we compare that to a full 1.00 ct. diamond at $5500 per carat, or $5500. You can quickly see that a .50 ct., diamond is more than twice the price of a .25 ct., diamond, and a 1.00 ct., diamond is more than double the .50 ct. diamond. Therefore a ring with a 1.00 ct. total weight, consisting of five .20 ct. diamonds (5 x .20 ct. = 1.00 ct.) would cost considerably less than a ring with a single 1.00 ct. diamond, even if all other quality factors were equal. And of course a 1.00 ct. total weight diamond ring made up of one hundred .01 diamonds would substantially less as well.
