A diamond's weight in carats is one measure of its value, along with the other 3 of the "4 Cs:" carat weight, cut, color and clarity. Diamonds are among the rarest of materials on earth; every diamond, of every size and quality, has a definite value.

The size of a diamond is measured in its carat weight. One carat = 1/5 of a gram. Carats are further divided into 100 points. Diamond weight may sometimes be expressed in points or in carats: a "75 point diamond" weighs 3/4 of a carat.

Large diamonds are far more rare than smaller ones. Large diamonds are highly prized because of their rarity and because larger diamonds, when cut, have more brilliance. Carat for carat, a large diamond will cost more than a smaller one.

It is difficult to judge the carat weight of a diamond by its apparent size; diamonds of the same diameter may weigh more or less than each other because of the way they are cut