The carat weight of a diamond helps to determine its cost. The Rappaport price list sets the guidelines for Dallas diamonds and diamonds around the world. You may see some diamonds that are priced above this list, and this is because of the exceptional quality of the stones above and beyond the carat weight.
The higher the price per carat (or PPC), the higher the cost of a diamond. You can expect to pay more than twice as much for a 2-carat diamond than for a 1-carat diamond. This is because the price is not necessarily determined solely in relation to the carat weight. Diamonds that are on the upper end of the quality spectrum for color and clarity will be more expensive, though stones that are cloudy or milky are not priced by this list simply because the quality is not there.