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 “cts.” One metric carat (abbreviated “ct.”) is one-fifth (0.200) of a gram—just over seven thousandths (0.007) of an ounce. One ounce contains almost 142 carats.
The metric carat is divided into 100 points. A point (abbreviated “pt.”) is one hundredth of a carat. An easy way to remember this is to think of carats as dollars and points as pennies. They’re even written the same way: $1.34 means one dollar and 34 cents, and 1.34 cts. means one carat and 34 points.
Diamonds are weighed to at least 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 dollars, depending on the quality of the gem.
Diamond weights over a carat are usually expressed in carats and decimals. A 1.03-ct. stone, for example, would be described as “one point oh three carats,” or “one oh three.” Weights for diamonds under a carat are usually stated in points. A diamond that weighs 0.83 ct. is said to weigh “eighty-three points,” or described as an “eighty-three pointer.”
The second aspect of carat weight that surprises people is the relationship between rarity, weight, and value. People expect a pound of sugar to cost twice as much as a half pound of sugar. But diamonds aren’t sold like sugar. Their prices depend on a number of variables—weight is just one of them. So it’s not always easy to understand, or explain, why a 1.00-ct. diamond is worth, say, $6,000, while a 2.00-ct. diamond of similar quality might be worth $15,000.
It’s really a simple concept: Large diamonds are rarer than small ones. You’ve already seen the relationship between rarity and value. The more scarce something is, the more it’s worth. So a larger stone doesn’t just cost more. It also costs more per carat. A 1.00-ct. diamond weighs the same as four 0.25-ct. 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 difference between a 0.98-ct. diamond and a 1.01-ct. diamond is almost invisible, many people will choose the larger stone—even at a much higher price. You’ll learn more about this in Assignment 5.
Don’t confuse the term carat with karat. Karat is a unit of measure that describes the purity—or fineness—of gold.
