How big is that gemstone, really?
Carat is a unit of weight, not size. Choose a stone type and shape below to see the actual dimensions at any carat weight.
Sapphire and ruby are denser than diamond, so they look slightly smaller per carat. Emerald is lighter than diamond, so it looks noticeably larger per carat at the same weight. Shape matters too — elongated cuts like oval, pear, and marquise look larger face-up than round or square cuts of equal weight.
| Carat | Dimensions (mm) | Depth (mm) |
|---|
These figures use the same weight-estimation approach gemologists use for mounted stones: Weight = Length x Width x Depth x Specific Gravity x Shape Factor. Sapphire and ruby (corundum) have a specific gravity of 4.00; emerald (beryl) is 2.72; diamond, for comparison, is 3.52 — which is why the same carat weight looks different across stone types. Figures assume standard well-proportioned cutting; a specific stone can vary from these numbers by a small margin depending on its individual proportions.
At 1.00 carat round, here's how the three stones compare in diameter:
~6.4mm
~6.5mm
~7.3mm
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