The carat is the standard unit of measurement used to indicate the weight of diamonds and precious gemstones. Since 1913, carat weight has been gauged against the metric system, with one carat equaling 0.2 grams or 0.007 ounces. Carat weight is measured to three decimal points and rounded to the nearest hundredth.
Carat Size Viewer
Rollover a diamond carat grade button to view its illustration.
Carat Weight and Price
Mined from deep within the layers of the Earth's crust, most rough diamonds are either too small or too inferior in quality to produce the lustrous, polished products demanded in the fine jewelry market. Consequently, the production of a single, one-carat diamond can require the mining of up to one million rough diamonds. The rarity of larger, high-quality diamonds has resulted in significant price escalations between sizes. For instance, a one-carat diamond can command four to six times more than a half-carat diamond.
Selecting a Carat Weight
Both carat size and quality should be taken into account when selecting a diamond. Below are some points to consider when choosing which carat weight is right for you:
Diamond pricing is determined by carat weight, and broken down in half-carat increments. Therefore, assuming factors like cut and clarity are equal, a diamond weighing one carat will cost more than a diamond weighing slightly less than one carat.
While its carat measurement indicates the weight of a diamond, its length and width measurements indicate the actual physical size, or how big the diamond will appear when viewed from above. Diamonds of the same carat weight can vary in size. For example, a one-carat round diamond could measure 5.9 mm in diameter, while another one-carat round diamond could be 6.5 mm wide. Broader diamonds with larger millimeter measurements create greater visual impact.
The price of a diamond rises as the carat weight increases. If carat weight is the most important factor in your search, consider a diamond with a clarity grade of Slightly Included (SI1-SI3) and a color grade of Near Colorless (G-J).
The shape of a diamond may impact how the stone appears when viewed from above. Diamond shapes cut at lower depths will have larger lengths and widths. Shapes like oval or marquise will have elongated lengths, resulting in the illusion of a larger size per carat weight.
When choosing a carat weight, be sure to consider the ring size of the wearer. A one-carat diamond will appear larger on a size-5 finger than it would on a larger hand.
If you have already chosen a ring setting or have one in mind, you may be restricted to certain diamond shapes and carat ranges.
The origin of the word -carat- lies in the Mediterranean region, where carob trees have flourished since ancient times. The seeds of the carob tree were once used as units of measurement against which diamonds were weighed. One carob seed is roughly equivalent to one modern carat, the word we use today to describe the weight of diamonds.
In the Far East, diamonds were historically weighed against grains of rice, resulting in the coining of the term 'grainer'. Today, gemologists still quantify the weight of diamonds in grainers. A four-grainer diamond is equal to one carat.