About Carat Weight : Diamond Education
The most obvious factor of a diamond's value is its size. However, two diamonds of equal size can have completely different values because of the other C's (listed above). As with all precious gems, the weight or size of a diamond in measured in carats. One carat is equal to 200 milligrams. When weighing diamonds, a 1.00 carat is divided into 100 points; therefore, a diamond of 25 points is also described as 0.25 carats or a quarter of a carat. As a diamond increases in size, its rarity increases, which also increases the price-per-carat exponentially. Therefore, a two-carat diamond is more than twice as valuable than a one-carat diamond of the same quality and characteristics.