Understanding Diamond Carat Weight

The term “Carat” refers to the weight of a diamond. This measurement is one of The Four “C”s used to determine diamond quality. It is derived from the carob seeds that were used to balance scales in ancient times because of their uniformity of weight and shape.

Carats are also the measure of weight for most gems, with one Carat equaling approximately 200 milligrams (0.2 grams). There are 142 carats to an ounce. Carats are further divided into points, with one Carat equaling 100 “points.”

Some common Carat weights, and their corresponding “points,” include:

  • One Carat = 100 points
  • Three-quarters Carat (3/4 Carat, 0.75 Carat) = 75 points
  • Half-Carat (1/2 Carat, 0.50 Carat) = 50 points
  • Quarter Carat (1/4 Carat, 0.25 Carat) = 25 points
  • Melee – tiny stones used in pave or channel settings. Usually
    weigh 0.15 carats (15 points) or less and are either grouped
    together or used to augment a larger stone.

Carat weight, combined with girdle diameter (the girdle is the outermost edge of a cut diamond), expresses the exact size of a diamond. Here are some notable Carat weights and the corresponding girdle diameters for round, ideally proportioned, brilliant cut diamonds:

  • 10 carats = 14 millimeters
  • 5 carats = 11.1 millimeters
  • 2.5 carats = 8.8 millimeters
  • 1 Carat = 6.5 millimeters
  • 0.75 Carat (3/4 Carat) = 5.9 millimeters
  • 0.50 Carat (1/2 Carat) = 5.15 millimeters
  • 0.375 Carat (3/8 Carat) = 4.68 millimeters
  • 0.25 Carat (1/4 Carat) = 4.1 millimeters
  • 0.125 Carat (1/8 Carat) = 3.25 millimeters
  • 0.0625 Carat (1/16 Carat) = 2.58 millimeters

All properties being equal, larger diamonds are rarer than smaller ones and are therefore more expensive. For instance, a one-Carat stone will generally cost much more than a 95 pointer. But other factors such as cut, color and clarity come into play as well in determining a stone’s value. It’s entirely possible for a  smaller stone of exceptional cut, color and clarity to be worth more than a larger stone of only average quality in these other areas.

It is this balance of preserving the greatest possible weight from the original rough diamond vs. producing a stone with the best possible quality in terms of cut, color and clarity that presents the most difficult challenge to the diamond cutter. Therefore, it is the cutter’s experience and skill that is the determining factor in preserving the beauty of a diamond while maintaining its size and value – and it is the cutter’s job to give you, the consumer, the finest quality stone, and largest Carat weight, for your money.