CARAT WEIGHT: A carat is equal to 1/5 th of 1 gram, or 0.007 of an ounce.

PRICE PER CARAT: Multiply the price per carat dollar amount by the diamond’s weight for the total and final cost:

Weight x Price per Carat = Total Price

The "price per carat" is established by a four factor examination:

1. WEIGHT

For simplicity's sake, diamond weights are broken in the following groups:

The price per carat in diamonds of the same color, clarity, cut quality and shape goes up with each weight group.

The following table demonstrates the relationship between weight and dimensions in round diamonds.

There is an important factor to consider when dealing with carat weight. A diamond with a higher carat weight, i.e a heavier diamond may not look larger than a similar diamond with a lower carat weight. Since a diamond is in reality a three dimensional object a disproportionate part of the weight may be lying on the bottom of the stone - away from the viewers eye. This is what is called a "deep stone" in the diamond trade.
As an example it is very possible that a round diamond that weighs 0.90 carats will look larger than a round diamond that weighs 1 carat.
Thus always look at the diamonds' measurements as well as the carat weight. When it comes to "what you see" the measurements are more important than the carat weight.
A diamonds depth percentage is basically the correlation between how deep the diamond is and how large it will look. The lower the depth percentage the larger the diamond will look in most diamonds. The exception to this rule is in long diamonds such as marquise shapes.
So, always look at the weight, measurements and depth percentage to get an indication of what the diamond will look like when it is set.
You very well may find a cheaper smaller diamond that looks as big or bigger than the diamond you thought you wanted to purchase at first

The better they are the higher the price per carat.

A better cut results in higher price per carat.

More expensive shapes yield higher price per carat.