The carat is the traditional unit of measurement for a diamond’s weight. Moissanite is not measured in carats because it weighs approximately 10 percent less than diamond. For example, a 6.4mm round diamond would weigh 1.00ct, while a 6.4mm round moissanite would weigh 0.88ct. Therefore, moissanite is typically categorized by its millimeter size rather than carat weight to avoid confusion. In this guide, we refer only to the carat sizes of diamonds.

Carat measures a diamond’s weight, not its size. One carat equals 0.2 grams, about the weight of a paper clip.

While many people may assume that a higher carat number means a larger center stone, the actual physical size of a diamond also depends on its cut and shape. In other words, two gemstones of the same carat weight can look drastically different in size, depending on how they are cut.Carat is one of the four key factors that define a diamond’s quality and value. It’s important not to confuse it with “karat,” which measures the purity of gold.

How Big is a Carat?

It is important to note that carat weight does not necessarily denote size. Different gemstones have different densities, moissanite stones are about 15 – 18% lighter than diamonds. Therefore, while a 6.5mm round diamond weighs 1.0 carat, a 6.5mm moissanite weighs 0.83 – 0.85 carats. However, the two stones would be the same actual size: 6.5mm in diameter.Factors like shape, cut, and depth also affect how large a gemstone looks. Keep in mind that every gemstone is unique, so carat weight can appear differently depending on the stone.

How Is Diamond Carat Measured?

One carat weighs 0.2 grams or 0.007 ounces. A stone weighing 1 gram would be 5 carats. Now that’s a big chunk of diamond! Diamonds are also referred to in points. 1 carat is 100 points, while a half-carat diamond might be called a 50-pointer diamond.

Diamond Carat vs. Diamond Size

Many people confuse carat weight with the size of the gemstone. While carat weight gives an idea of how heavy the diamond is, size is actually determined by the diamond’s shape and cut. Therefore, a “1-carat diamond” could appear quite different depending on whether it is cut in a round, oval, or emerald shape. A diamond’s cut also influences how well it reflects light, further affecting its visual appeal.

Diamond Carat Chart

This chart provides an estimate of the average size of different diamond shapes at various carat weights. Each image represents a top-down view of the diamond.

You may notice that two diamonds with the same carat weight can look different in size. This is because a diamond’s shape, along with its density and depth, significantly affects how its carat weight appears.

How Carat Affects Value

Diamonds are typically priced per carat, but the price doesn’t increase linearly as carat size increases. Larger diamonds are much more valuable because they are rarer in nature, so the price per carat increases dramatically as the carat weight grows. For example, a 2-carat diamond would be valued higher than two 1.0-carat diamonds of the same quality. Therefore, understanding the relationship between carat weight and price can help you determine the best diamond for your budget.

You may notice that two diamonds with the same carat weight can look different in size. This is because a diamond’s shape, along with its density and depth, significantly affects how its carat weight appears.