Diamond carat weight is commonly confused with the shape of the diamond. But diamond carat is used to measure a diamond's weight. It is also commonly confused with "karat" which is the measure of purity of gold. A carat equals 0.2 grams or 0.007 ounce. A diamond's price is determined by its carat weight and the price per carat
Total Price = Weight x Price per Carat.
Since a carat is a unit of measure and not size, two diamonds of the same carat weight may appear to be different sizes depending on how the diamond is cut. Some diamonds will have extra weight on the bottom part - or pavilion - of the stone, and therefore appear smaller. A premium cut Canadian diamond is perfectly cut, and will appear larger than many diamonds of a heavier carat weight.
The term carat originated in ancient times when gemstones were weighted against the carob bean. Each bean weighed about one carat. In 1913, carat weight was standardized internationally and adapted to the metric system. One carat equals 0.2 grams (200 milligrams) - a little more than 0.007 ounce. In other words, it takes 142 carats to equal 1 ounce.
According to the Gemological Institute of America (GIA) the history of how using the carat for weighing diamonds and small items came out is as follows. Weighing commodities as small and precious as gems demands a very small, uniform unit of weight. To meet this need, early gem traders turned to plant seeds that were reasonably uniform in size and weight. Two of the oldest were wheat grains and carob seeds. Both were common in the gem-producing and trading areas of the ancient world. Wheat was a dietary staple, and individual wheat grains provided a plentiful and relatively uniform weight standard.
Our modern Pearl grain, troy grain, and avoirdupois and apothecaries' grains all derived from the wheat grain. (Diamond weights are sometimes approximated in grains) The carob, or locust tree, produces edible seed pods that are still important as feed for livestock and as a flavoring. Traders used the inedible seeds as a standard weight from which our modern metric carat evolved. All other things being equal, the greater the carat weight, the rarer the diamond and the more expensive it is. Although bigger is assumed to be better, diamonds of all carat weight have equal charm.
To choose ideal carat weight, there are a few things to remember. Consider doing the following to optimize your carat weight while balancing the other 3 Cs to get the best diamond value for the money: