The shapes compared
| Shape | Sparkle | Looks big for the weight | Price per carat |
|---|---|---|---|
| Round brilliant | Highest | Baseline | Highest |
| Oval | High | Much larger | Lower than round |
| Pear | High | Larger | Lower |
| Marquise | High | Largest | Lowest of the brilliants |
| Cushion | High, softer | Slightly smaller | Lower |
| Princess | High | Smaller | Lower |
| Radiant | High | About the same | Lower |
| Emerald | Broad flashes, not sparkle | Larger | Lower |
| Asscher | Broad flashes | Smaller | Lower |
| Heart | High | Slightly smaller | Lower |
Brilliant cuts versus step cuts
Almost every shape on that list is a brilliant cut, meaning it uses triangular and kite shaped facets arranged to bounce light back at your eye as many small bright flashes. Round, oval, pear, cushion, princess and marquise all work this way.
Emerald and asscher are step cuts. Their facets run in long parallel rows like steps, and instead of scintillation you get broad flashes and a sense of depth. They are quieter stones, and because there is nowhere for an inclusion to hide, they demand a higher clarity grade than a brilliant of the same money.
The bow tie, and where to look for it
Elongated brilliants, so ovals, pears and marquises, are prone to a dark band across the middle called a bow tie. It is a light leakage effect caused by the proportions, it appears on almost every stone in these shapes to some degree, and no certificate grades it.
A faint one is normal and disappears as the stone moves. A pronounced one is a permanent dark patch in the centre of the diamond. This is the single reason you should never buy an oval or a pear without seeing it, or at minimum watching a video of it moving in light.
Choosing by what you care about
Maximum sparkle: round brilliant, and pay for an Excellent cut grade.
Maximum apparent size for the money: oval. It is both cheaper per carat and larger face up than a round.
Understated: emerald cut, but budget for a higher clarity grade because the open table shows everything.
Not sure what you are looking at?
Photograph the stone and the app gives you a visual read on the 4Cs, an estimated value range, and what to check next. Free on iOS and Android.
Frequently asked questions
Which diamond shape looks the biggest?
Which shape sparkles the most?
Why are round diamonds more expensive?
Do fancy shapes get a cut grade?
Worth being clear: everything here, and the app itself, is an educational reference. At-home tests narrow things down, they do not certify a stone. Before you buy, sell or insure anything of real value, get it looked at by a certified gemologist or an independent appraiser.