A carat is a unit of weight for diamonds and other gems. The metric carat of .200 grams, or 200 milligrams was adopted in the United States in 1913 and now standardized in the principle countries of the world.
The weight of a diamond is numerically expressed in carats. Diamond weight is subdivided further into smaller units commonly referred to as points. A point is a scale of weight that is equal to .01 carat. A one carat diamond is made up of 100 points. The term point(s) does not refer to the amount of facets or individual flat surfaces a diamond possesses as its definition is sometimes incorrectly interpreted.
A diamond that weighs .50 carats or 50 points would be considered 1/2 carat in size. A diamond that weighs 1.00 carat or 100 points is considered a carat. A two carat diamond would weigh 2.00 carats, 200 points or 400 milligrams.
It is very important that one does not relate the numerical values of carat weight as a judgment of a diamonds actual diameter size. Because carat weight is a numerical value of weight, it is therefore possible for a diamond with a smaller diameter to weigh the same or more than a diamond with a larger diameter. This is done by making the smaller diamond deeper or thicker and the diamond with the larger diameter is made shallower or thinner. See diagram to the right.
Unfortunately, many people buying diamonds today are unable to recognize inferior cut diamonds, and as a result , many diamonds sold today are inferior in cut. Diamond cutters have a substantial financial incentive not to remove any more weight from the rough diamond crystal than they feel is necessary to sell the diamond. Because cutters are able to deliver a heavier diamond from a smaller rough diamond crystal, he is able to sell the diamond for less and make more profit.
For example: An ideal or very fine cut one carat diamond will measure 6.4 to 6.5 millimeters. If you were to measure the diameters of one carat diamonds on the market today, you would find many that measure between 5.9 and 6.3 millimeters. These inferior cut, "under-size diamonds" would have only the diameter of ideal cut or fine cut diamonds that weigh .75 to .99 carats. These diamonds are not truly a one carat from the standpoint of diameter and acceptable brilliance.
You must also realize that a degree of brilliance is sacrificed when diamonds are produced with inferior cut. Comparing an ideal cut or very fine cut diamond to an inferior cut diamond is similar to comparing a 100 watt light to a 50 watt light. The 50 watt looks acceptable until it is compared to the 100 watt light. The diagram above illustrates the path light takes through an inferior and ideal cut.
"Inferior cut diamonds" are abundant in all size ranges and are commonly sold with GIA, EGL and IGI and other diamond quality reports. Because GIA, EGL, IGI and other gemological laboratories do not assign an overall cut grade, it is up to the individual to know a diamonds depth percentage, table percentage, girdle thickness, culet, polish, symmetry and more. Please refer to detailed information contained in the previous page that describes details of a properly cut diamond.