Diamond Carat Weight

The easiest of the four Cs to understand is that of carat weight.

It's simply the weight of the stone itself, without the setting. In the trade, the prices of diamonds are expressed in price per carat, and the diamond's size makes the largest difference.

The easiest of the four Cs to understand is that of carat weight. It's simply the weight of the stone itself, without the setting. In the trade, the prices of diamonds are expressed in price per carat, and the diamond's size makes the largest difference.

A carat is exactly 0.20 grams, or 200 milligrams, and there are 100 points per carat. The certified weight of the carat is always listed to two decimal places, but the machine that weighs them is accurate to one-thousandth of a gram (0.001), or three places.

Not all diamonds have the same price for the same weight. Each individual diamond, depending on its cut, color, and clarity, will fall into a particular category of price per carat. More desirable stones cost more, and while size is the biggest determining factor of price, a smaller stone of higher quality may cost the same.

A diamond's price, ultimately, depends on the price per carat category into which it belongs. Even then, the price per carat varies according to size. As of 2000, a diamond of a particular color and clarity will be in one price category if it's between 0.50 - 0.69 carats and will increase per carat if it's increased to the next size range, 0.70 - 0.89 carats. The next range, 0.90 - 0.99 carats increases in price again, in part because larger stones are simply more rare. Stones in the 1.00 - 1.49 carat range increase the price per carat significantly compared to the smaller ranges, and stones in the 1.50 - 1.99 carat range will show an additional cost per carat. The rest of the sizes, 2.00 to 2.99, 3.00 to 3.99, 4.00 to 4.99 and so on increase in price per carat respectively.