Carat is the term used to express the weight of a diamond, with one carat equaling 200 milligrams of actual weight.

Carat Abbreviations

• The abbreviation ct is a shortened way to write carat, and refers to the weight of a single diamond.
• The abbreviation ct TW means carat total weight, and is used to express the total weight of multiple diamonds used in a piece of jewelry.

Carat Weight vs. Size

Carat weight is used as a measure for other gemstones, but different gems of the same weight aren't necessarily the same size, because some gemstones are more dense than others -- they pack more weight into a smaller space.

Weight of Small Diamonds

The weight of smaller diamonds is often expressed as points instead of carats -- there are 100 points in a carat.

Another way to look at it is to say that each point equals 0.01, or one-hundredth, of a carat.
Point Examples

• 0.05 means five one-hundredths, so a 0.05 carat diamond equals five points.
• 0.25 means twenty-five one-hundredths, so a 0.25 carat diamond equals twenty-five points, or one quarter of a carat.

How Carat Weight Affects Value

Larger diamonds are more rare and in more demand than smaller diamonds of the same quality. A one carat diamond solitaire ring is nearly always more expensive than a diamond ring made up of multiple diamonds that are similar, but smaller, even though they total one carat or more.
Diamonds that weigh just under the next full carat are typically less expensive than diamonds passing the full-carat hurdle. In her interview for About Jewelry, Antoinette Matlins offered this opinion about carat weight:

• "...try to find a diamond that weighs 90-points (9/10ths carat), rather than a full 1-carat, or 1.90 carats rather than a full 2-carats, and so on. When set, no one can see the difference, but you'll enjoy a big savings in cost."

How to Compare Diamonds

Diamond comparisons are useless unless they're made among diamonds with similar qualities and features.

• Considering the price per carat is a good way to compare the costs of similar diamonds. Divide the cost of each stone by its carat weight to calculate its price per carat.

There is no single visual diagram that can illustrate diamonds of different carat weights, because variations in shape and cut make stones of similar weights look very different. A diamond weight estimator, a sheet with cutouts for different diamond shapes and sizes, can help give you a preview of how a diamond's size relates to its carat weight.

Carat weight is only one diamond characteristic that you should explore before you buy a diamond. Take some time to understand more diamond basics before you go shopping.