Diamond Shape Guide

Jewelers say "princess cut" and "emerald cut", so the confusion is understandable — but shape and cut are two different things. Shape is the outline of the stone viewed from above: round, oval, pear and so on. Cut is a quality judgment: how well the facets are angled, sized and polished so that light entering the stone bounces back to your eye instead of leaking out of the sides. Two ovals with identical outlines and identical carat weights can look completely different on the hand if one is cut well and the other is cut deep and dull.

The distinction shows up on the certificate, too. IGI — the laboratory that certifies Signora's lab-grown diamonds — states an overall cut grade, from Excellent down to Poor, for rounds and fancy shapes alike. (GIA, by long-standing convention, reserves its overall cut grade for the round brilliant.) Treat the grade as a starting point rather than the whole verdict: for the nine fancy shapes it sits alongside polish, symmetry, the length-to-width ratio and the millimeter measurements, and those numbers tell you how the stone actually carries its weight. That is why this guide keeps pointing you back to measurements. If the grading language is new to you, our stone guide walks through the 4Cs first.

Carat is weight, not size. What you actually see on the hand is spread — the face-up area of the stone — and spread depends on where the weight sits. A shallow, well-proportioned stone carries its weight across the top, where you can see it; a deep one hides weight below the girdle, where you cannot. This is why two 1.50 ct ovals can look half a size apart.

The length-to-width ratio describes how elongated a shape is: length divided by width. A ratio of 1.00 is perfectly square or round; 1.50 is half as long again as it is wide. There is no correct number — only classic ranges, listed for every shape below — and the millimeter measurements are printed on every IGI certificate. An oval measuring 7.7 by 5.7 mm, for example, has a ratio of about 1.35.

Round brilliant. Fifty-seven or fifty-eight facets arranged for one purpose: returning the most light possible. No other outline matches its brilliance, which is why it remains the reference point — a well-cut 1.00 ct round faces up at about 6.5 mm, with a ratio of 1.00–1.02. With no points or corners it is the most forgiving shape to wear and to set, and a straight wedding band sits flush beside most round solitaires. The trade-off is cost: cutting a round sacrifices more rough, so it carries the highest price per carat of any shape.

Oval. The same brilliant faceting, stretched. An oval faces up around 8–10% larger than a round of equal carat and elongates the finger; the classic ratio is 1.30–1.50. Watch for the bow-tie — a shadowy band across the middle of any elongated brilliant. A faint one is normal; a dark, fixed one is a reason to pass. There are no vulnerable points, so simple prongs or a hidden halo are plenty. See oval stones in the finder.

Cushion. A pillow outline with softly rounded corners and a warmer, chunkier sparkle — some cushions glitter in larger blocks, others in a fine "crushed ice" pattern. Cushions are usually cut deep, so they face up slightly smaller than a round. Ratios run 1.00–1.05 square, up to about 1.20 elongated. The rounded corners are naturally durable, and the shape suits vintage-style halos beautifully.

Step cuts trade glitter for glass. Long, parallel facets run in terraces down the stone, producing broad, unhurried flashes — the "hall of mirrors" — instead of a thousand tiny sparks. The effect is calm and architectural, and it is entirely honest: those big open facets act like windows, so inclusions and body color that a brilliant cut would scatter into invisibility stay plainly visible. Give a step cut higher grades than you would a brilliant — VS2 clarity or better, and a color grade or two whiter than you might otherwise accept.

Emerald. The rectangular classic, at its most elegant around a 1.30–1.45 ratio. Its spread is modest, but the long lines make it read larger than it measures. Its cropped corners exist for a practical reason: they remove the sharp points that would otherwise chip, which is why this shape has survived centuries of daily wear. Four corner prongs or a bezel suit it, and straight or baguette-set bands echo its lines perfectly.

Asscher. A square step cut with a deep pavilion and a windmill pattern radiating from the center. That depth makes it the smallest-facing of the ten shapes per carat — choose it for the geometry, not the spread. Like the emerald, its cut corners are self-protecting, and it pairs naturally with clean, straight bands.

Princess. Brilliant-style faceting folded into a crisp square — sharp geometry on top, plenty of fire underneath, ratio 1.00–1.05. Its weight sits deep, so it faces up smaller than a round of the same carat. The four uncut corners are the one genuine fragility among the square shapes: they concentrate stress and can chip if left exposed or clamped carelessly. Insist on a setting with chevron (V-shaped) corner prongs, a bezel, or a halo that wraps the corners. The reward for those straight edges is a perfectly flush stack with a straight wedding band.

Radiant. Take an emerald outline — cropped corners included — and fill it with brilliant faceting, and you get the radiant: dense "crushed ice" glitter in a square (1.00–1.05) or elongated (1.15–1.35) form. It is one of the most practical shapes of all: the trimmed corners are durable, the busy faceting is unusually forgiving of inclusions, and an elongated radiant gives real spread. If you love the emerald silhouette but want fireworks, this is the answer.

Diamond is the hardest material known, but hardness is resistance to scratching, not to impact — and a fine point concentrates any knock into a tiny area. Pears, marquises and hearts are not fragile stones; they are stones with one or two spots that must be covered by the setting. The cover is a V-prong: a folded prong that cradles the tip from both sides.

Pear. A teardrop — one rounded end, one point — with generous spread and a flattering, elongating line; classic ratios run 1.45–1.75. Like all stretched brilliants it can show a bow-tie, so judge each stone individually. Most people wear the point toward the fingertip, but there is no rule. A low-set pear sits happily beside a straight wedding band; a taller setting usually calls for a gently contoured one.

Marquise. Two points, and the largest face-up spread of any shape — a boat-shaped outline at a dramatic 1.75–2.25 ratio that elongates the finger more than any other. Both tips need V-prongs, without exception.

Heart. Two rounded lobes, a crisp cleft between them, and a point below — a shape that lives or dies on its symmetry. The outline reads clearly from about 1.00 ct upward; smaller than that, it can blur at arm's length. Set it with a V-prong at the point and a prong on each lobe.

A quick rule of thumb: every point or corner gets covered; every curve can go bare. Rounds, ovals and cushions are happy in simple four- or six-prong settings. Princess corners want chevron prongs or a wrapping halo. Pear, marquise and heart tips want V-prongs. Emerald, asscher and radiant carry their protection built in — their corners are already trimmed. And if your hands work hard, a bezel (a full metal rim) protects any shape completely, at the cost of a little light around the edge.

Then think one ring ahead. Straight-edged shapes — princess, emerald, asscher, radiant — sit flush against a straight wedding band. Rounds and ovals in low settings do too; the same stones over a halo or in a tall cathedral setting often leave a gap that only a contoured or curved band will close. We cover the pairing question in our wedding band pairing guide and the settings themselves in the settings guide.

Because every Signora piece is made to order, shape is a decision you make — not a compromise you inherit from a display cabinet. Choose any of the ten shapes in this guide as an IGI-certified lab-grown diamond, or as GRA-certified moissanite, which is cut in the same outlines (see how the two stones compare here). We then craft the piece around it in solid 925 silver, 9K, 14K or 18K gold, or platinum Pt950 — typically delivered in about 14 days, with duties prepaid to the US, UK and Canada.

Start with our loose diamond finder to browse certified stones by shape, carat and grade, or read the engagement ring guide for the full journey from idea to finished ring. Standard designs carry 30-day returns, and if you are torn between two shapes, a free consultation costs nothing and carries no obligation.