Diamond Carat Weight
Cut | Color | Clarity | Carat Weight
The weight of a diamond is traditionally measured in 'carats' (0.2g), based on the weight of a carob bean. For stones of equal quality, the higher the carat weight, the greater the value.
This is by far the easiest of the factors to understand. Simply put, smaller diamonds are more common than large ones. Therefore smaller diamonds cost less per carat than large ones.
Carat is a unit of measurement, it's the unit used to weigh a diamond. One carat is equal to 200 milligrams, or 0.2 grams. The word carat is taken from the carob seeds that people once used in ancient times to balance scales. So uniform in shape and weight are these little seeds that even today's sophisticated instruments cannot detect more than three one-thousandths of a difference between them. (Don't confuse it with 'karat', the method of determining the purity of gold.)
The process that forms a diamond happens only in very rare circumstances, and typically the natural materials required are found only in small amounts. That means that larger diamonds are uncovered less often than smaller ones. Thus, large diamonds are rare and have a greater value per carat. For that reason, the price of a diamond rises exponentionaly to its size.