Carat Weight

 The standardized unit used to measure the weight of diamonds and most other precious gemstones is called the carat.  The carat is equal to 0.200gr, or 200 mg.  The weight of a diamond can also be expressed in points.  1 carat is equal to 100 points.  This means that a diamond that weighs 0.100gr is a ½ carat diamond, or a 50 point diamond. The abbreviation for carat is ct. 

The word carat comes from the Greek, “keration”, meaning carob seed.  For hundreds of years, Mediterranean merchants believed that carob seeds were uniform in weight, and therefore they were used as a reliable unit to measure the weigh of small, valuable materials such as diamonds and precious gemstones.  Carob seeds, while not exactly uniform in weight, are very close to it.  Try weighing them yourself at home and you’ll find that most seeds will weigh in around 0.200 grams!  In the early 1900s, the United States diamond industry decided to standardize the carat against the metric system as 0.200 grams to the carat, and the standardized carat was soon adopted internationally.

Carat weight may be an indicator of diamond size, but isn’t accurate or reliable. Because a diamond is typically viewed from above, diamonds with bigger diameters, or larger faces, usually appear larger than diamonds with smaller diameters.  However, some diamonds have a shallow cut.  This means that their face or diameter is large, while the pavilion, or faceted cone that hangs below, is short.  These diamonds may appear to be larger when set in jewelry or viewed from above, but their carat weight may be surprisingly low.  Conversely, diamonds with a deep cut that feature a small face or diameter and a long pavilion may appear smaller when set in jewelry or viewed from above, and yet their carat weight may be surprisingly high. Additionally, diamonds that are have high scintillation; fire and brilliance also seem bigger due to their impressive light return.   Despite the inaccuracy, there is still a general correlation between carat weight and diamond size.  Check out Zoara's Carat Weight Tool to get the idea of the diamond's increase in size as related to its carat weight. 

The price of a diamond jumps dramatically with increase in carat weight because of the great value of rough diamond material. Because large diamonds are so rare (one in approx. 1,000,000 diamonds mined produces a full 1 carat diamond), the bigger the diamond, the more expensive it will be.  A diamond jumps in price at every .50 ct mark.