Despite often being referred to as Emerald “Cut” or Princess “Cut,” shape is the outline of a diamond, which differs from the “Cut” from the 4Cs. Compare actual measurements and video, and make sure the setting protects any corners or points.
Diamond shapes at a glance
| Shape | Facet style | Looks for its weight | Hides inclusions | Setting notes |
|---|---|---|---|---|
| Round | Brilliant | Standard | Very well | Easiest to set |
| Oval | Brilliant | Larger | Well | Watch for bow-tie |
| Cushion | Brilliant | Slightly smaller | Well | Softened corners |
| Princess | Brilliant | About the same | Well | Protect four corners |
| Radiant | Brilliant | About the same | Very well | Cropped corners, durable |
| Emerald | Step cut | About the same | Less well | Needs higher clarity |
| Pear | Brilliant | Larger | Well | Protect the point |
| Marquise | Brilliant | Largest | Well | Protect both points |
Length-to-width ratio chart
Length-to-width ratio is how long a stone is compared to how wide it is. Divide the length by the width from the report. A ratio of 1.00 is perfectly square or round. Higher numbers are more elongated.
| Shape | Popular range | What it looks like |
|---|---|---|
| Round | 1.00 to 1.02 | Circular |
| Princess | 1.00 to 1.05 | Square |
| Cushion (square) | 1.00 to 1.05 | Pillow-shaped square |
| Cushion (elongated) | 1.15 to 1.30 | Soft rectangle |
| Radiant (square) | 1.00 to 1.05 | Square with cropped corners |
| Radiant (rectangular) | 1.20 to 1.35 | Rectangle with cropped corners |
| Oval | 1.30 to 1.50 | Classic oval |
| Emerald | 1.30 to 1.50 | Rectangle with step facets |
| Pear | 1.45 to 1.75 | Teardrop |
| Marquise | 1.75 to 2.25 | Long football shape |
These are popular ranges, not rules. A 1.25 oval looks fuller and rounder, and a 1.60 oval looks long and slim. Pick the outline you like best.
Round and oval
Round brilliants are cut to return as much light as possible, and they're the most popular engagement ring shape. Their cut grading is the most established of any shape, which makes them the easiest to compare. They cost more per carat than most fancy shapes because cutting a round loses more of the rough crystal.
Ovals have the brilliance of a round in an elongated outline, and they look noticeably bigger for their weight. The thing to watch is the bow-tie, a darker band across the middle that shows up in most ovals to some degree. A faint one is normal. A strong one is distracting. Judge it in video with the stone moving, not in a single photo.
Cushion, princess and radiant
Cushions have a square or rectangular outline with rounded corners, like a pillow. Facet patterns vary a lot. Some show broad flashes of light, and others (often called "crushed ice") show a finer, glittery sparkle. Two cushions with the same grades can look completely different, so the video matters most here.
Princess cuts are square with sharp, pointed corners and a lot of sparkle. Those corners are the weak spot. They can chip if hit, so the setting needs prongs covering each one.
Radiants combine a square or rectangular outline with cropped corners and brilliant faceting. They're lively, hide inclusions well, and the clipped corners make them more durable than a princess.
Emerald
Emerald cuts are step cuts. Instead of lots of small sparkly facets, they have long, parallel facets that create broad flashes of light. People sometimes call it a "hall of mirrors" look. It's elegant and quieter than a brilliant cut.
Those open facets work like windows, so inclusions and body color are easier to see. For an emerald cut, lean toward VS1 or higher clarity, and look closely at the video. The clarity guide explains why.
Pear and marquise
Pears are rounded at one end and taper to a point at the other. Marquise diamonds taper to a point at both ends. Both look large for their weight and elongate the finger.
Both can show a bow-tie like an oval. Check symmetry too. The two sides should mirror each other and the point should line up with the rounded end. The points are the most fragile part, so the setting should protect them, usually with V-prongs.
Which shapes look biggest
Because carat is weight, shapes that spread their weight across the top look larger than shapes that carry weight deep. Roughly, from largest-looking to smallest for the same carat weight:
- Marquise
- Oval and pear
- Round, princess, radiant and emerald
- Cushion, which often carries more depth
If you want the most visible size for your budget, an oval, pear or marquise gets you there.
Compare the stone, not just the shape name
Carat is weight. Face-up length and width are what people see. For non-round shapes, two stones of the same weight can have very different outlines.
IGI doesn't issue a cut grade for every shape, and the details on a report can vary with report type and date. So compare the exact dimensions, proportions, polish and symmetry, and the video, rather than assuming the shape name tells you how a stone will look.
- Choose an outline and length-to-width ratio you like.
- Compare millimeter measurements alongside carat weight.
- Watch the stone in video from several angles and in different light.
- Ask your jeweler to confirm the prongs, basket fit and protection for corners or points.