The One Carat Diamond

A carat is a unit of weight, not size: one carat is 0.2 grams. The word comes from the carob seed, once used as a counterweight on gem scales. Because it measures weight, two one carat diamonds can look quite different in size, depending on their shape and how they are cut.

Approximate face-up measurements for a well-proportioned one carat diamond. Actual sizes vary with each stone’s proportions:

Elongated shapes such as the marquise, pear and oval cover the most finger for their weight. Square step cuts such as the Asscher carry more weight in their depth and look smallest from above. Our carat page shows sizes across other weights.

Diamond prices rise sharply at popular weights, and 1.00 carat is the most popular of all. A 0.90 carat stone can look almost identical on the hand to a 1.00 carat, but cost noticeably less, because it sits below the threshold.

If the number itself matters to you, buy the full carat. If the look matters more, a stone just under it is one of the easiest ways to stretch a budget.

Put cut first: a well-cut one carat diamond looks larger and brighter than a poorly cut one, which can hide weight in its depth. Then choose colour and clarity you cannot see: G to H colour looks white in platinum or white gold, and an eye-clean VS2 is usually enough in a brilliant shape. Always buy with an independent grading report.

A one carat lab-grown diamond costs a fraction of a natural one of the same grade, so for the same budget you can choose a higher grade or a larger stone. A natural one carat diamond is rarer and holds value better. Our natural vs lab guide gives the honest case for each.