A carat is equal to 200 milligrams (one fifth of a gram) or 1/142nd of an ounce. Ben Bridge uses scientifically accurate electronic diamond scales which weigh diamonds to 1/200th of a carat. Carat weight is also expressed as "points". A one carat diamond is 100 points, therefore a ½ carat diamond is .50 ct. and is referred to as "50 points". Diamond weights can be rounded off to fractions,( ¼ carat, ½ carat for example), but when an exact weight is used, the reference is made as "53 points" for example and is written as 0.53 ct. A common misconception is that carat weight is a unit of size, it is not. It is a unit of weight. This is why you may see 3 diamonds that all weigh one carat (1.00 ct) but they all may appear to be a different visual size from one another. One may be 6.0mm in diameter if it is cut deeper than another which will be 6.5mm in diameter or if one diamond is cut very shallow it may be 6.8mm. How the diamond is cut will greatly affect the beauty and brilliance of the diamond as well as the price. For more information read about Cut and Ideal Cut Diamonds. As diamonds increase in size, the value increases geometrically, rather than arithmetically. A one-carat diamond can easily be worth five times as much as a half-carat diamond of the same quality.
Gemstones are sold by weight, not by size or volume. This significant difference makes them more like gold and silver than other luxury products, such as furs, yachts, automobiles, or watches. Since gems are comprised of different chemical elements, they do not all weigh the same. Therefore, gemologists use weight as one means of identification.
Weight, or density, is expressed as specific gravity (SG). Diamond has an SG of 3.52, which means a diamond weighs 3.52 times as much as the same volume of water. In comparison, emeralds are lighter, with an SG of 2.72. Because each gem has its own specific gravity, gem sizes vary considerably compared with other stones of the same weight. With equal weights, emeralds are larger than diamonds; rubies and sapphires are smaller.
Gems are weighed in carats (not to be confused with "karat," which refers to the purity of gold). A carat, from the ancient Indian use of carob seeds for small consistent weights, equals 1/5 gram, or 1/142 ounce. Sizes are measured in millimeters (see below). A round one carat diamond, a standard weight in the trade, is typically 6.5mm in diameter. A round one carat ruby or sapphire, being denser, measures about 6.1mm across; a round one carat emerald is usually 6.6 to 6.7mm.
Cutting proportions for diamonds are normally much more standardized than for colored gems. When buying diamonds, the main factors that determine price are the four Cs: carat weight, color (or lack of color), clarity, and cut. When in doubt, consult an expert. With diamonds, it pays.
The Sales Associates at Ben Bridge Jewelers are trained and qualified to answer your questions and explain the differences between individual diamonds. Please visit one of our store locations to see our extensive selection of fine quality jewelry.