Elongated Radiant Cut Diamond Guide: Ratio, Size, Colour and Settings

What is an elongated radiant cut diamond?

A radiant cut is a rectangle or square with its four corners trimmed off, faceted like a brilliant rather than in the long, flat steps of an emerald cut. Gemmologists call it a cut-cornered rectangular modified brilliant. A modified brilliant uses the triangular and kite-shaped facets of a round brilliant, rearranged to suit a different outline. Most radiants have about 70 facets, which gives a busy, lively sparkle. For the shape as a whole, start with our complete guide to radiant cut diamonds.

"Elongated" simply means the stone is clearly longer than it is wide. A radiant with a length-to-width ratio of roughly 1.00–1.05 looks square, and our guide to square radiants and how they differ covers those. Once the ratio passes about 1.20, the rectangle reads clearly from across the room, and that is the stone this page is about.

The radiant was developed by cutter Henry Grossbard and introduced in the late 1970s. It was designed to give a rectangular stone the brightness of a round. Before that, rectangles were mostly step cuts, which show clean, mirror-like flashes but hide less. Diamond itself is 10 on the Mohs hardness scale, with a refractive index of about 2.42, the reason brilliant faceting returns so much light.

The elongated radiant belongs to the wider family of long and slender diamond shapes such as oval, pear and marquise, and you can see where it sits among all the outlines in our introduction to diamond shapes. Unfamiliar terms are explained in the GemTrove jewellery glossary.

What is the best ratio for an elongated radiant cut diamond?

The length-to-width ratio is the length of the stone divided by its width, both taken from the measurements on the grading report. A 7.00 × 5.20 mm radiant has a ratio of 1.35. There is no correct number, but the ratio decides whether the stone looks gently rectangular, classic or long and narrow.

As a rule, a higher ratio makes the stone look larger from above for the same weight, because more of it is spread along the finger. Above about 1.50, though, the narrow width can make the centre look darker and the corners more pronounced. Our ratio guide for radiant diamonds shows photographed examples at each step.

Do elongated radiant diamonds have a bow-tie?

Often, yes. A bow-tie is a dark band across the middle of an elongated stone where light leaks out of the pavilion (the lower half) instead of bouncing back to your eye. A faint bow-tie that flickers as the stone moves is normal and adds contrast. A solid dark band that stays put in every position means the proportions are off.

GIA does not give radiants an overall cut grade, so you judge them on proportions and appearance. As a rough guide, many well-cut elongated radiants sit at:

• Depth: about 61–69% of the width. Deeper than about 70% and the stone carries hidden weight and looks small face-up.
• Table: about 61–69% of the width. The table is the large flat facet on top.
• Girdle: thin to slightly thick, with no extremely thin areas at the cut corners.
• Polish and symmetry: Very Good or Excellent on the report.

Radiants also differ in faceting style. Some show a crushed ice look, many small, glittery flashes that read almost like fragments of ice. Others have larger, more defined flashes, closer to a princess cut; our princess and radiant comparison explains that difference. Neither is better; it is a matter of taste, and photos rarely capture it, so watch a 360° video.

How big does an elongated radiant look? Size chart

Radiants are cut fairly deep compared with ovals or pears, so they look a little smaller face-up than some other shapes of the same weight. That makes the millimetre measurements more useful than the carat figure when you compare stones. Face-up size means the outline you see when you look down at the ring.

These are typical figures only; a shallower stone of the same weight spreads wider and a deeper one looks smaller. Two 1.00 ct elongated radiants can differ by half a millimetre or more in length, which you will notice on the hand. From about 0.70 carat the rectangle reads clearly; below that, radiants work well as side stones or in earrings.

What colour and clarity should an elongated radiant have?

Radiants hold colour more than rounds. The brilliant facets and the deep pavilion concentrate body colour, and in an elongated stone it tends to gather at the ends and the cut corners. In white gold or platinum, most people are happy from H colour or better, and G if you are sensitive to warmth. In yellow or rose gold, I or J usually looks white once set.

For clarity, aim for eye-clean: no inclusions (internal features) visible without magnification at normal viewing distance. The radiant's busy faceting hides small inclusions far better than the open table of an emerald cut, so a well-chosen SI1, or VS2, is usually enough. Check the plotting diagram on the report for feathers (small internal cracks) near the corners, the thinnest part of the stone.

• White metal: G–H colour, VS2–SI1 eye-clean.
• Yellow or rose gold: I–J colour, VS2–SI1 eye-clean.
• Coloured diamonds: the radiant is a favourite for fancy yellow, because the faceting intensifies colour.

How does an elongated radiant compare with emerald, cushion and oval?

The closest relative is the emerald cut: same outline, very different light. Our emerald vs radiant guide sets them side by side, and the elongated emerald cut guide covers the step-cut version in detail. If you want a softer outline, the long cushion cut has rounded corners, and how radiant and cushion cuts differ explains the trade-offs.

Many people end up choosing between a long cushion and an oval as well; see ovals against elongated cushions and, if you are still deciding how long you want the stone, square or elongated cushions compared. The same thinking applies to radiants.

What is the best setting for an elongated radiant cut engagement ring?

The cut corners make a radiant tougher than a princess cut, which has sharp points. That gives you more freedom in the setting. Common choices for an elongated radiant cut engagement ring:

• Four claws: one on each cut corner. The classic choice; it shows the most of the stone and keeps the corners covered.
• Double claws: two claws at each corner, eight in total. More secure and gives a slightly softer frame.
• Hidden halo: a ring of small diamonds under the stone, visible from the side only.
• Full halo: small diamonds around the outline, making the stone look larger.
• Three-stone: trapezoid, baguette or half-moon side stones suit the straight sides.
• East-west: the stone set sideways across the finger, a modern look that suits ratios of 1.40 and above.
• Bezel: a rim of metal around the edge. Very secure, but hides a little of the outline.

See radiant engagement ring styles for examples and setting ideas for long diamond shapes for how claws, halos and bezels change the look. Because the straight sides sit close to a band, most radiants pair easily with a straight wedding ring; our guide to choosing a wedding band for a radiant ring covers the exceptions, such as low-set halos.

How much does an elongated radiant cut diamond cost in Australia?

Elongated radiants are cut from both natural and laboratory-grown diamond. A lab-grown diamond is real diamond, with the same hardness and refractive index, grown in a laboratory rather than mined. It costs much less than a natural diamond of the same grades and is easy to find in larger sizes. Natural radiants are rarer. Both should come with an independent report from a lab such as GIA or IGI that states clearly whether the stone is natural or lab-grown.

These are broad ranges only; prices move with the market and the exact grades. Radiants usually cost less per carat than rounds, because more of the rough crystal is kept when cutting. Within radiants, carat, colour, clarity and how well the stone is cut move the price most; ratio itself makes little difference, though very well-proportioned elongated stones in popular ratios can cost a little more.

How do you choose an elongated radiant cut diamond? Step by step

1. Read the report. Confirm shape, measurements, colour, clarity, polish, symmetry and whether the diamond is natural or lab-grown.
2. Work out the ratio. Divide length by width; most people prefer about 1.25–1.40.
3. Check depth and table. Aim for roughly 61–69% for each, and avoid stones deeper than about 70%.
4. Watch a 360° video. Look for a bow-tie that stays dark, and decide whether you prefer crushed ice or larger flashes.
5. Compare millimetres, not carats. Two stones of the same weight can face up quite differently.
6. Check colour at the ends. Look for warmth gathering at the short ends and corners.
7. Plan the setting. Choose claws or a bezel that cover the corners, and think about the wedding band at the same time.