Carat Weight is how much your diamond weighs. Over a carat, diamond weights are usually expressed in carats and decimals. Visually, there's little difference between a 0.99 ct. But the price differences between the two can be significant. The aspect of carat weight that surprises people is the relationship between rarity, weight, and value.
People know that a pound of sugar costs about twice as much as a half pound of sugar.
So it's not always easy to understand, or explain, why a 2.00-ct. The scarcer a diamond is, the greater its worth. So a larger stone doesn't just cost more. It also costs more per carat. Remember, as big a factor as carat weight may be, like the other three Cs, no one of them is automatically more important than the others.