Shape is the first thing most people decide and the last thing most guides explain properly. It is not the same as cut. Shape is the outline. Cut is how well the facets are proportioned within it.
Shape affects price, apparent size, how visible inclusions are, and how the stone behaves in light. Here is how the main ones differ.
Brilliant cuts and step cuts
Almost every shape falls into one of two families, and the distinction matters more than the outline itself.
Brilliant cuts use triangular and kite shaped facets arranged to bounce light back at the viewer. They sparkle, and that visual busyness hides small inclusions well.
Step cuts use long, parallel, rectangular facets arranged in tiers, producing broad flashes rather than sparkle. The effect is often called a hall of mirrors. Because the facets are large and open, inclusions are far easier to see, so step cuts generally need a higher clarity grade to look clean.
That single fact should shape your budget. A step cut at a low clarity grade will show what a brilliant cut would have hidden.
The main shapes
Round brilliant. Fifty seven or fifty eight facets, engineered specifically to maximise light return. It is the most brilliant shape and the most popular by a wide margin. It is also the most expensive per carat, because cutting a round from rough discards more material than any other shape.
Oval. A brilliant cut, elongated. It carries its weight across a larger face-up area than a round of the same carat, so it looks bigger for the money. Elongated brilliants can show a bow tie, a dark band across the centre caused by the setting blocking light. A slight one is normal, a heavy one is a cutting fault worth avoiding.
Emerald. The classic step cut. Rectangular with cut corners, understated, and dependent on clarity. It suits people who want elegance over sparkle, and it should be bought eye clean.
Asscher. Essentially a square emerald cut, with the same step cut character and the same clarity requirement.
Princess. A square brilliant cut. Strong sparkle, and cheaper per carat than a round because it wastes far less rough. The sharp corners are the vulnerable point and want a setting that protects them.
Cushion. A softened square or rectangle with rounded corners. Warmer and less sharp than a princess, and a common choice for fancy coloured stones because the shape concentrates colour well.
Radiant. A rectangle with cut corners and brilliant faceting, combining the outline of an emerald cut with the sparkle of a brilliant. It also hides inclusions better than a true step cut.
Pear and marquise. Elongated brilliants that look large for their weight. Both can show a bow tie, and both need symmetry checked carefully, since an off centre point is immediately obvious.
Shape affects price
Round brilliants cost the most per carat. The reason is waste: cutting a round from a rough crystal discards a great deal of material, and that loss is priced in.
Shapes that follow the natural form of rough more closely, particularly princess and cushion, retain more weight and cost less per carat as a result. Choosing a shape other than round is one of the more reliable ways to get a larger stone for the same money.
Apparent size
Carat is weight, not size, and shape changes how much of that weight you actually see.
Elongated shapes such as oval, pear and marquise spread their weight across a wider face-up area, so they look larger than a round of identical carat. Deeper shapes hide weight below the surface where nobody sees it.
Our guide to the 4Cs covers why cut quality matters more than any of this.
Choosing one
Maximum sparkle: round brilliant. Maximum apparent size per dollar: oval or another elongated brilliant. Understated and architectural: emerald or Asscher, bought eye clean. Best value per carat with strong sparkle: princess or cushion.
There is no ranking here. Shape is the one genuinely personal decision in buying a stone.
Frequently asked questions
What is the difference between shape and cut?
Shape is the outline, such as round or oval. Cut is how well the facets are proportioned, which determines how the stone returns light.
Which diamond shape is most expensive?
Round brilliant, per carat, because cutting a round discards more rough material than any other shape.
Which shape looks biggest for the carat?
Elongated shapes such as oval, pear and marquise, because they spread weight across a wider face-up area.
What is a bow tie in a diamond?
A dark band across the centre of an elongated stone, caused by light being blocked. A faint one is normal, a strong one indicates poor cutting.
Do emerald cuts need higher clarity?
Yes. Step cuts have large open facets that make inclusions far more visible than brilliant cuts do.
Our diamonds
We hold certified lab grown and natural stones. See the range or read how to buy a diamond in New Zealand.