Diamond Carat Weight

Diamonds and other gemstones are weighed in metric carats: one carat is equal to 0.2 grams, about the same weight as a paperclip. (Don’t confuse carat with karat, as in “18K gold,” which refers to gold purity.)

Just as a dollar is divided into 100 pennies, a carat is divided into 100 points. For example, a 50-point diamond weighs 0.50 carats. But two diamonds of equal weight can have very different values depending on the other members of the Four C’s: clarity, color and cut. The majority of diamonds used in fine jewelry weigh one carat or less.

Because even a fraction of a carat can make a considerable difference in cost, 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.  Diamond weights greater than one carat are expressed in carats and decimals. (For instance, a 1.08 ct. stone would be described as “one point oh eight carats,” or “one oh eight.”)



Diamond illustration not actual size

A few gems of wisdom:

  • Although diamond carat weight influences cost quite a bit, when determining diamond size, always consider the distance in millimeters across the top (as that is how diamonds are presented when set in a ring), as well as the cut grade.
  • If sparkle is more important, start with cut, color, and clarity first before choosing a carat weight.
  • If size is more important, and budget is a concern, consider a stone with a higher diamond carat size and lower clarity and/or color rating.
  • Consider “under sizes” which are diamonds that weigh just below the full and half carat weights. They represent a very good value, as small size differences are hard to visually detect.