Carat Weight

When you ask someone what they want in a diamond, usually the first thing they’ll say is big. So let’s talk first about carat weight.

What is a carat? We already know it’s a measure of weight, not size, but it’s also a word with a fascinating history. Carat is derived from carob, the bean that’s often used as a chocolate substitute.

Carob trees grow in the Mediterranean region, and in ancient times a diamond of one carat, or carob, was equal in weight to a single bean, or seed, of the carob tree. In the Far East, rice was used — four grains equaled one carob bean.

Eventually the carat was standardized at 200 milligrams (1/5 of a gram), and the grain was standardized at 50 milligrams. Sometimes you will hear a diamond dealer refer to a one-carat diamond as a four-grainer. Diamond weights are also referred to in points. One carat equals 100 points, so a 75-point diamond would weigh 3/4 of one carat. (It’s not a diamond with 75 points on it, as some people think!)


You’ve no doubt heard or seen the marketing slogans, “A diamond is forever;” “Say you’d marry her all over again with a diamond anniversary ring;” and “A one carat diamond is one in a million.” These all come from ad campaigns by DeBeers, the world’s largest diamond conglomerate. Through their clever marketing they have established the one-carat diamond as the minimum size to buy. That’s one reason for the substantial price jump when a diamond reaches one carat. Another reason is that a good one-carat diamond is one in a million. But don’t be swayed by advertising. There’s no magic in size, and the average diamond purchased in the U.S. is 38 points — just over 1/3 of a carat.

by Fred Cuellar, author of the best-selling book “How to Buy a Diamond.” More questions? Ask the Diamond Guy®.

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