Diamond Size Chart

A well-cut 1.00 carat round diamond measures about 6.5 mm in diameter. The same carat weight looks different across shapes — a 1ct oval is roughly 7.7 × 5.6 mm and a 1ct princess about 5.5 mm — because carat measures weight, not size.

Carat is a unit of weight. How large a diamond looks face-up depends on its shape and how it is cut. A shallow or elongated cut spreads the weight across a wider top and looks bigger, while a deep cut hides weight below the girdle and looks smaller. That is why cut quality matters as much as carat.

Because a diamond’s weight scales with its volume, its width scales with the cube root of carat. Our tool anchors each shape’s dimensions at 1 carat and scales from there, so you can enter any carat weight and see the approximate mm size and a true-to-scale preview.

Elongated shapes such as marquise, oval and pear have a larger face-up area per carat than round or princess cuts, so they appear bigger for the same weight. Marquise typically looks the largest, which is why these shapes are popular for maximizing visual size on a budget.

It can be. Screens vary in pixel density, so the tool includes a one-time calibration: hold a standard bank card against the on-screen bar and drag the slider until they match. After that, the diamond preview renders at its real physical size.