A carat is a weight measurement used for gems, equaling 200 milligrams.
Carat weight began with the carob seed, when early gem traders used the small, uniform seeds as counterweights in their balance scales.
A carat is divided into 100 points. ½ carat = 50 points, or 0.50 carat. Diamond weights greater than one carat are expressed in carats and decimals.
Diamond price increases with diamond carat weight because larger diamonds are rarer and more desirable. Visually, there’s little difference between a 0.99 carat diamond and one that weighs a full carat. But the price differences between the two can be significant.
The other components of the 4 C’s affect the price between individual stones. Two stones of the same size can have very different price tags!
Examples of various carat sizes (not shown actual size):