Pricing diamonds per carat is how most wholesalers quote diamond prices. For example, one might say he has a 1.25-carat diamond for $3000.00 per carat. To find the total cost, multiply the per-carat price by the weight. In this case, $3000.00 X 1.25ct = $3750.00.
The degree of rarity in a diamond is reflected in its per-carat price.
The quality of a round brilliant cut has to do with the way light enters and exits the stone. A well-cut diamond will reflect light more than any other type of shape (square, oval, pear and so on).