Carat: The 4C's Of A Diamond Explained


Carat (ct) ...

Carat (ct) is a weight only. Carat should never be judged as an indication of quality!

Many goods are sold by weight — by the kilogram, ounce, pound, or ton. Even people who have never bought a diamond are used to the idea that weight and price are related. They understand that a larger diamond is probably more valuable than a smaller one. But there are two things that often surprise people when they start learning about diamonds and carat weight.

The first is the precision with which diamonds are weighed. Diamond weights are stated in metric carats, abbreviated “ct.” One metric carat is two-tenths (0.2) of a gram—just over seven thousandths (0.007) of an ounce.
The metric carat is divided into 100 points. A point is one hundredth of a carat.

Diamonds are weighed to a thousandth (0.001) of a carat and then rounded to the nearest hundredth, or point. Fractions of a carat can mean price differences of hundreds—even thousands—of pounds, depending on diamond quality.
Over a carat, diamond weights are usually expressed in carats and decimals. A 1.03-carat stone, for example, would be described as “one point oh three carats,” or “one oh three”. Weights for diamonds that weigh under a carat are usually stated in points. A diamond that weighs 0.83 carat is said to weigh “eighty-three points”, or called an “eighty-three pointer”
The relationship between rarity, weight and value can be surprising. People know that a pound of sugar costs twice as much as a half-pound of sugar. But diamonds aren’t a commodity like sugar. Their price depends on a number of variables—weight is just one of them. So, it’s not always easy to understand, or explain, why a 1-carat diamond is worth, say, £6,000, while a 2-carat diamond of similar quality might be worth £15,000.

It’s really a simple concept: Large diamonds are rarer than small diamonds. The scarcer something is, the more it is worth. So, a larger stone doesn’t just cost more. It also costs more per carat. A 1-carat diamond weighs the same as four 0.25-carat diamonds. But even if all the other quality factors are equal, the larger diamond is worth much more than the sum of the four smaller diamonds.

Carat weight can also be symbolic. While the visual difference between a 0.98-carat diamond and a 1.01-carat diamond is negligible, many people will opt for the larger stone—even at a much higher price. Some weights are considered “magic sizes”: half carat, three-quarter carat, one carat, etc. There’s not much difference in their weights, but if both are D-colour round brilliants with identical clarity and cut, the size makes all the difference. They really don’t look much different, but if your heart is set on the one-carat size, the difference is enormous. The fact that the second gemstone is slightly over the “magic” one-carat size can give it as much as a 20 per cent difference in price with only a 6-point difference in weight.

The chart below can give a rough comparison of carat size to millimetres.