Diamond carat

What does carat mean?

Carat is a unit of weight, not size. One carat equals 0.2 grams. The term comes from the carob seed, which was historically used as a counterweight because of its consistent mass.

Why carat weight matters

Carat weight is one of the biggest factors in a diamond's price. As carat weight increases, price rises disproportionately because larger rough diamonds are harder to produce.

Carat weight alone does not determine how large a diamond looks. Two diamonds of the same weight can appear different sizes depending on their cut proportions and shape. A well-cut diamond will often look larger and brighter than a poorly cut stone of the same weight.

For a deeper look at how carat weight is assessed, see IGI's carat weight guide.

Common carat sizes compared

Here are approximate diameters for round brilliant cut diamonds at common carat weights. These give a useful sense of scale when comparing options.

Actual dimensions vary depending on cut quality and shape. Elongated shapes like oval or marquise tend to look larger than a round diamond of the same carat weight because their surface area is spread differently.