Foundations
Diamond Shapes
How each outline behaves in the light, which proportions matter, and how shape influences perceived size.
Shape describes the outline of a diamond when viewed face-up. It is the first decision most buyers make, because it sets the character of the stone before any grading term enters the conversation.
Shapes fall broadly into two families. Brilliant cuts — round, oval, pear, marquise, radiant, cushion and princess — use triangular and kite-shaped facets to scatter light into bright flashes. Step cuts such as emerald and Asscher use long parallel facets that produce broad, mirror-like reflections and a quieter, more architectural look.
Spread and perceived size
Two diamonds of identical carat weight can look noticeably different in size. Elongated shapes such as oval, marquise and pear distribute weight across a larger face-up area, so they typically appear larger than a round of the same weight. Deeper shapes such as princess and cushion carry more weight below the girdle.
Length-to-width ratio
For any non-round shape, the length-to-width ratio determines how elongated the diamond appears. Preference is personal, but the ranges below are commonly considered classic.
- Oval — 1.35 to 1.50
- Emerald — 1.30 to 1.50
- Marquise — 1.85 to 2.10
- Pear — 1.45 to 1.70
- Radiant — 1.00 to 1.35
- Cushion — 1.00 to 1.20