Diamond Carat Guide

Our Diamond Carat Guide walks you through all the basic information you need to know about diamond carats.  The carat is the weight of a diamond. And karat is the measure of purity of the gold ring that holds the diamond. A carat is equal to 0.20 grams. Although diamonds of a high carat weight are larger than others, the carat indicates weight and not the dimensions of a diamond. Diamond size is measured by length, width, and depth in millimeters. A good measure of the rarity of diamonds is that to get 1.00 carat of diamond a miner needs to excavate 250 tons of rock.

Because diamonds are so rare, a diamond cutter tries to preserve as much of the diamond, the carat weight, as possible. Diamonds are cut in numerous shapes but sometimes a certain cut is used precisely to retain the most carat weight possible. The higher the carat of the diamond, the rarer and more expensive it is. Diamond weight is measured to the 0.01 carat. Anywhere in the world where diamonds are bought and sold the carat is the universal standard for weight. This was not always true. Before the metric carat was adopted as a diamond weight standard in 1907, there were several systems in use. In the far past, diamond weight was measured on a balance scale using carob seeds. The belief was that carob seeds were very uniform in weight. This, however, was not really the case. Because of its accuracy and reproducibility, the carat became, in time, the international standard for diamond weight no matter who certifies a diamond.

How to Tell The Size of a Diamond

Once you know the carat weight of a diamond you may wish to know its size. The width, length, and depth of a diamond are measured in millimeters. And, with a round cut, the width and length are the same as they are the diameter of the diamond. Also, there is the appearance of size and there is real size. A diamond may be cut round, but with less depth. This diamond will appear larger than a diamond cut to greater depth. This is because its diameter is greater and that is often the first thing that people notice.

And round cut diamonds are less deep than many of the fancy (non-round) cuts. As an example, a round cut diamond of 1.00 carat will have a diameter of about 6.40 millimeters. A Princess cut of the same carat may measure about 5.50 millimeters. The take-home point here is that fancy cuts appear smaller at a given carat weight than a round cut. The result is that round cuts are typically more expensive than fancy cuts for the same carat size.

Even for expert gemologists, it can be difficult to see a difference of 5% to 10% in carat weight. This, of course, is why we weigh them! To get a diamond of a given carat that looks larger it can be cut more shallow but wider. This may simply be a result of the shape of the rough stone or it may be a choice of the diamond cutter. The problem here is that there are specific dimensions that are best for diamond sparkle, brilliance, and fire to show to their maximum. Cutting a diamond outside of these ideal dimensions may result in a larger gem but it may reduce the brilliance of the diamond.

For more insight take a look at our diamond size chart expressed in millimeters.

Diamond Sizes in Millimeters

Carat and the Price of the Diamond

As the carat size of a finished diamond goes up so does its rarity, and its price. As with other factors that determine the value of a diamond, price does not go up one for one with increases in size. The price increases multiple in what is called an exponential fashion. There are a series of so-called critical carat weights at which price bumps occur. These start at every 0.10 carat from 0.30 carat up to 1.00 carat. Then the price bumps occur at 1.50 carat, 2.00 carat, 3 carat, 4 carat, 5 carat, and 10 carat.

Now that you know what the critical weights are at which diamond prices rise, you can plan your purchase by staying at the top of, but still within, a given carat range. Let’s say that you want a 1.0 carat diamond. Providing that color, cut, and clarity are similar, you will get what you want with a 0.95 carat diamond as well as with a 1.05 carat diamond. Even a professional gemologist will not be able to tell the difference in size between this diamond and one of exactly one carat. And your pocketbook will thank you!

Many folks shopping for a diamond think of carat first. They want a large and impressive diamond. If this is you, think as well of the other factors. Depending on your budget you may need to reduce the quality of the cut, clarity grade, or color grade in order to afford a larger stone. Likewise, if what you want is the best in color, brilliance, and cut, you will need to reduce carat in order to come in at a price you want to pay or can simply afford.

Take a look at our chart that estimates diamond price by carat. You will see that the price per carat goes up with heavier diamonds. If the price per carat doubles and the carat weight doubles, then you are looking at a four-fold price increase. Also, take a look at the photos showing how diamonds of increasing carat look in comparison to a normal woman’s fingers. These photos will give you a good first idea of how the diamond will appear when worn on an engagement ring. Be sure to consider the size of the hand that will wear the diamond as well as the size of the diamond. Also, fancy cuts will look bigger than round cuts so keep that in mind as well. And, finally, remember that when the diamond is set in a ring, the setting increases the size of the presentation as well.

Carat Weight and Final Price

To get an idea of how much you will pay for a larger diamond carat weight look at this carat weight versus price chart. It shows how price increases exponentially with larger carat size. This chart is for round diamonds of 1.00, 2.00, and 3.00 carats.

Tips For Buying a Diamond from the Diamond Experts

Critical weight cutoffs are important. Try to find diamonds with carat weight just below the critical level at which the price per carat jumps up. Shop for 0.95 carat diamonds if what you want is one carat.

Look for well-cut diamonds in any carat weight. Such diamonds are usually not so deep and therefore are broader. This diamond will look larger than one cut to greater depth and less spread.

If, like most people, carat weight is most important to you, shop for carat first and then look at cut, color, and clarity. But, always remember that a really large diamond with flaws will not be all that impressive. Make sure to balance carat weight with color, clarity, and cut.