Blog, Buyer's Guide

Diamonds: Carat


Diamonds and other gemstones are weighed in metric carats: one carat is equal to 0.2 grams, about the same weight as a paperclip. The term karat, as in “18K gold” on the other hand, refers to the purity of the gold.

A carat is divided into 100 points;  for example, a 50-point diamond weighs 0.50 carats. Two diamonds of equal carat weight may have very different values, however, depending on the cut, color and clarity of each diamond. In nature, large diamonds are actually very rare; most diamonds used in fine jewelry weigh one carat or less.

Even a fraction of a carat will effect the diamond’s cost, so precision is crucial. In the diamond industry, weight is often measured to the hundred thousandths of a carat, and rounded to a hundredth of a carat. A diamond will only be rounded up to the nearest hundredth if the thousandth digit is a 9. For example, a diamond that weights 1.768 cts. would be rounded to 1.76 cts., but one that weighs 1.769 cts. would be rounded to 1.77 cts. Diamond weights greater than one carat are expressed in carats and decimals, e.g., a 1.08 ct. stone would be described as “one point oh eight carats,” or “one oh eight.”

How did the carat system start?

There appears to be a long history of associating carat weight with the carob seed, perhaps due to the seed’s fairly uniform size and weight (the evidence for this is more anecdotal than factual, however). The ancient Greeks had a small weight, the kerat, while the siliqua (from the Latin for carob, siliqua Graeca) was the smallest subdivision (1/1728) of the Roman pound. The ancient carat most likely originated from these measurement systems. The modern metric carat, equal to 0.2 grams, was adopted by the United States in 1913 and other countries soon after. Today, a carat weighs exactly the same in every corner of the world.

The measure of gold purity—the karat, also has its roots in ancient history; it derived from the time of Emperor Constantine when a new gold coin was struck at 72 to the Roman pound, meaning each coin weighed 24 siliquae or carats.

How  important is carat weight when buying a diamond?

The short answer is: not as much as the most important factor which is the diamond’s cut.

Ultimately, a diamond is all about looks, brilliance, fire, and scintillation. These characteristics are primarily determined by the diamond’s cut. Only a diamond with Excellent cut proportions will provide you with the maximum brilliance you should initially look for. However, a diamond with an exceptional cut AND more carat weight will make the facets of the diamond appear larger which will also return more light and sparkle to the viewer’s eye.

Our advice is to make sure you start with the best possible cut and then adjust the carat weight accordingly based upon your budget. Too often, people focus on carat weight first and want the prestige factor of having a diamond of at least 1 carat in weight. In some cases, in order to make that diamond affordable buyers will compromise on the cut—we want to help you avoid that happening if possible!