Diamond shapes and cuts: which one to choose

In jewelry, the word "cut" covers two things: the outline of the stone seen from above (round brilliant, oval, pear, princess…) and the quality of its execution (proportions, symmetry, polish). This guide presents the nine shapes offered by the diams.com diamond search engine, what each one does with light, what it shows or hides, and what to read on its GIA report. In GIA vocabulary, any shape other than round is a "fancy shape".

1. The round brilliant: the reference

A round brilliant has 57 or 58 facets, the 58th being the culet, a tiny facet at the tip of the pavilion. Its geometry, crown, girdle and pavilion, is organized to return light to the eye; it settled at the end of the 17th century and was formalized by optics in the early 20th century, with Marcel Tolkowsky's Diamond Design (1919). A 1 carat brilliant measures about 6.4 mm across.

It is the only shape that receives a GIA cut grade, from Excellent to Poor, because its facets are standardized. The grade assesses the brightness, fire and scintillation of the stone seen face up, its proportions, its durability and the ratio of its weight to its diameter, as well as its polish and symmetry. diams.com selects round brilliants graded Excellent to Very Good, with no fluorescence. It is also the most represented shape in the engine: round brilliant diamonds.

2. The elongated shapes: oval, pear and marquise

These three shapes use the brilliant faceting. For the same weight, they show a larger surface than a round and look bigger; set along the finger, they lengthen it. All of them show a "bow-tie", a dark area across the center of the stone: when light, it belongs to the shape and adds depth; when wide and black, it kills the stone. It depends on the pavilion proportions and is best judged in hand or on video, under several lights.

The oval diamond has no corner and no point, which makes it less exposed to knocks than the other fancy shapes. Most ovals have a length-to-width ratio of 1.3 to 1.4; longer stones, preferred in a 2009 GIA survey (1.7), are rarer because they are harder to cut from the rough. Regular shoulders, neither flat nor bulging, give a harmonious outline.

The pear diamond combines a rounded end and a point. Many specialists prefer a ratio of 1.50 to 1.75. The point is the most fragile part: a V-prong or a bezel protects it, and an inclusion near the point is to be avoided. A pear holds more color than a brilliant, so it is wise to choose high on the color scale.

The marquise diamond, or navette, originated in France in the 18th century; legend attributes it to Louis XV, around 1740, in honor of the Marquise de Pompadour. The classic proportion is twice as long as wide; marquises submitted to GIA most often measure 1.6 to 2.2. Both points are protected by V-prongs, and the symmetry of the wings can be checked at a glance.

3. Square and rectangular shapes with brilliant facets: princess, radiant and cushion

The princess is a square with sharp corners, cut with a modified brilliant faceting; developed in 1979, it is, according to GIA, the second choice for engagement rings after the round brilliant. A square princess does not exceed a ratio of 1.05; rectangular ones generally stay below 1.25. The corners, exposed to chipping, are protected by V-prongs or a bezel.

The radiant, created in 1977, combines a rectangular or square outline with cropped corners and a brilliant faceting. Its facets disguise inclusions better than those of an emerald cut, which allows a lower clarity grade. To check: a centered culet, parallel sides and four corners cropped to the same size.

The cushion has slightly curved sides and rounded corners, square or rectangular; it is the heir of the old mine cut, one of the oldest. Its faceting varies from one stone to another: some cushions have a fire close to the brilliant, others a softer glow. Opposite sides must mirror each other exactly. The shape is particularly suited to colored diamonds.

4. The step cut: the emerald

The emerald cut is a rectangle with beveled corners whose crown and pavilion carry rows of parallel facets. It produces less scintillation than a brilliant faceting; in return, the color of the stone and its inclusions are more visible. It therefore calls for a high color and a high clarity, both read on the GIA report. It is the most common of the step cuts, associated with the Art Deco style; it is also worn across the finger, east-west.

5. The heart

The heart diamond is judged first by its symmetry: the two lobes, the cleft and the point must match on both sides, with a length-to-width ratio of 1 to 1.2. Below half a carat, the outline is hard to read. Clarity characteristics are easier to see than in other shapes, and the point calls for a setting that protects it, a halo for instance.

6. Reading the GIA report of a fancy shape

A fancy shape receives no cut grade, but its GIA report gives everything needed to judge it: the measurements in millimeters, from which the length-to-width ratio is calculated, the depth and table in percent, the girdle thickness, the culet, then polish and symmetry, graded from Excellent to Poor, and fluorescence. The diamonds in the engine come with their GIA report. The four criteria themselves are explained in our 4Cs guide, and the choice of a stone for a ring in our solitaire guide.

7. What the engine offers

Survey of November 8, 2026 in the engine, for diamonds of 1.00 to 1.49 ct, color G, clarity VS2: number of stones available and lowest price, in CHF including VAT, GIA report included. Market prices can move at any time; each link opens the current list.

Shape	Stones	Lowest price
Round brilliant	81	CHF 4,170
Oval	58	CHF 4,250
Pear	60	CHF 4,250
Princess	50	CHF 4,250
Marquise	50	CHF 4,250
Radiant	52	CHF 4,250
Emerald	53	CHF 4,250
Cushion	58	CHF 4,300
Heart	54	CHF 4,250

At equal weight, color and clarity, the prices of the fancy shapes in the engine are close to those of the round brilliant; the difference lies in the number of stones available and in the choice of the shape itself. Orders of magnitude by weight and quality are in our price guide.

Further reading: Diamond search engine · Guide to the 4Cs of diamonds · How to choose a solitaire · Diamond prices · Diamond solitaires · gemmologue.ch, Le diamant, Book III, cut shapes (in French) · GIA, the cut grade