Choosing a stone before the setting is the smartest way to build a ring. When you buy lab grown diamonds loose, you control the shape, carat weight and quality, and you only pay for what you actually want. The trouble is that shape changes everything, from how big the diamond looks to how much sparkle it throws.

Here is the short answer. The six diamond shapes most UK buyers choose are round, oval, cushion, emerald, pear and princess. Round gives the most brilliance, which makes it the best diamond shape for sparkle. Oval and pear look larger for their carat weight. Emerald and cushion suit a vintage or understated style. Whichever you pick, insist on a grading certificate from a recognised lab such as IGI or GIA, so you know the cut, colour and clarity are what you are paying for.

Below, we walk through each shape and who it suits best. We are a family-run jeweller in Hatton Garden, and we set loose lab-grown diamonds in bespoke rings every week, so the advice comes from the workbench, not a catalogue.

1. Round brilliant lab grown diamonds

The round brilliant is the shape most people picture when they think of a diamond, and it remains the top seller among loose lab grown diamonds in the UK. It is the safest choice if you want maximum sparkle with no fuss.

What it looks like and how it sparkles

With 57 or 58 facets, the round brilliant is engineered to return light straight to your eye. That gives it the most brilliance of any shape, and it also hides small inclusions well, so you can often drop a clarity grade without seeing any difference.

Cut decides how a round performs. Ask for an Excellent (or Ideal) cut grade with Excellent polish and symmetry, because a shallow or deep stone leaks light and looks flat, however good the colour is.

On a round diamond, the cut grade matters more than colour or clarity.

Who it suits

Choose a round if you want a classic solitaire that never dates, such as a round cut diamond engagement ring. It suits traditional and modern settings alike, from a simple four-claw to a hidden halo. It is also the easiest shape to match with a wedding band, because it has no points to catch and no gaps to leave.

Be aware that a round looks smaller face-up than an oval or pear of the same carat weight. If size on the finger matters more to you than symmetry, look at those shapes instead.

Typical UK price and what to look for

Expect to pay the highest price per carat here, because cutting a round wastes more of the rough crystal. These are indicative prices for IGI-certified stones in E to G colour, VS clarity and Excellent cut. Lab-grown prices move often, so treat them as a guide.

Finally, when you buy loose lab grown diamonds UK retailers sell, check that the report number matches the laser inscription on the girdle. A good jeweller will show you the stone under magnification and explain the grading report line by line.

2. Oval lab grown diamonds

Oval is the shape we see most often after round. It gives you more apparent size for your money and a softer, more modern look.

What it looks like and how it sparkles

An oval has an elongated outline and a brilliant-style facet pattern, so it sparkles almost like a round. The catch is the bow-tie, a darker shadow across the centre that appears in most ovals. A faint one is normal. A heavy one looks dull.

Also check the length-to-width ratio. Between 1.35 and 1.50 gives a classic oval, and anything narrower looks stretched.

Judge an oval by its bow-tie and ratio, not only by the grade on the certificate.

Who it suits

Pick an oval if you want a larger-looking stone at the same carat weight as a round. The long shape also flatters the finger by making it look slimmer. It works well in oval engagement ring styles such as a solitaire or a hidden halo, and it has no sharp corners, so it is hardy enough for everyday wear.

Typical UK price and what to look for

Because less rough crystal is lost in cutting, ovals usually cost less per carat than rounds. These are indicative prices for IGI-certified stones in E to G colour and VS clarity.

When you buy loose lab grown diamonds in this shape, ask for a photo or video of the actual stone. Two ovals with identical grades can look very different, so you need to see the bow-tie before you commit.

3. Emerald cut lab grown diamonds

The emerald cut is the quiet option on this list. Its rectangular outline and stepped facets favour clean, glassy elegance over fireworks, and it is a favourite for art deco style rings.

What it looks like and how it sparkles

Instead of sparkle, you get long flashes of light and dark, often called a hall-of-mirrors effect. The large open table works like a window, so inclusions and tint show more easily than in a round.

Because of that, clarity matters here. Look for VS2 or better and E to G colour, and check the length-to-width ratio. Between 1.30 and 1.50 is the classic proportion.

An emerald cut hides nothing, so buy the clearest stone you can.

Who it suits

Choose an emerald cut if you like vintage or minimalist design. It looks striking as a solitaire or with baguette side stones, and the long shape slims the finger. The corners are cut away, which makes chipping less likely, though a claw on each corner is still wise.

Typical UK price and what to look for

Emeralds usually cost less per carat than rounds and look large for their weight. These are indicative prices for IGI-certified stones in E to G colour and VS clarity.

With lab grown loose diamonds in this cut, ask for a video before you commit. Eye-clean clarity and an even, well-proportioned outline matter more than the grade alone.

4. Cushion cut lab grown diamonds

The cushion cut is a square or slightly rectangular stone with rounded corners, like a pillow. It has a romantic, antique feel yet stays practical for everyday wear.

What it looks like and how it sparkles

Cushions come in two styles. A crushed ice cushion has many small facets and sparkles like glitter. A chunky cushion has larger facets and gives bolder, clearer flashes.

Because chunky cuts show more of the inside, choose VS2 clarity or better. For a square outline, look for a length-to-width ratio of 1.00 to 1.10.

Always ask which cushion style you are buying, because the two look very different.

Who it suits

Pick a cushion cut diamond engagement ring if you want a soft, vintage look without losing sparkle. It sits well in a halo, a three-stone ring or a plain solitaire, and the rounded corners make it resistant to chipping.

Colour shows more in cushions than in rounds, so stay at E to G colour for a white stone. A cushion also looks a little smaller than an oval of the same carat weight.

Typical UK price and what to look for

Expect prices close to oval, since cutting wastes a moderate amount of rough. These are indicative prices for IGI-certified stones in E to G colour and VS clarity.

When you buy loose lab grown diamonds in the UK, ask for a video of the actual stone and get the cushion style confirmed in writing.

5. Pear shaped lab grown diamonds

The pear, or teardrop, joins a rounded end to a tapered point. It is the most distinctive shape on this list, and it suits anyone who wants a stone that stands out from the usual solitaire.

What it looks like and how it sparkles

Pear stones use a brilliant facet pattern, so they sparkle much like an oval. They also show a bow-tie shadow, and the point should sit sharp and centred over the rounded end. Aim for a length-to-width ratio of 1.45 to 1.75 for a balanced teardrop, because anything shorter looks stubby.

A pear is only as good as its point, so check that it is sharp, centred and well protected.

Who it suits

Choose a pear diamond engagement ring if you want a larger-looking stone for your carat weight and a lengthening effect on the finger. It works in a solitaire, a halo or a pendant-style ring. The point is the weak spot, so ask your jeweller for a V-shaped claw to guard it, and wear the ring with the point facing your nail.

Typical UK price and what to look for

Expect prices a little below oval, as cutting a pear wastes less rough. These are indicative prices for IGI-certified stones in E to G colour and VS clarity.

Before you buy loose lab grown diamonds UK sellers list as pears, ask for a video of the actual stone. Check that the point is not chipped and that both shoulders curve evenly, because uneven shoulders make the stone look lopsided.

6. Radiant cut lab grown diamonds

The radiant is the best of both worlds, with the rectangular outline of an emerald and sparkle closer to a round. If you like the look of a princess cut, it is the sturdier alternative.

What it looks like and how it sparkles

A radiant has trimmed corners and a brilliant-style facet pattern, so it throws far more fire than an emerald cut. The busy facets also hide small inclusions and tint, which means VS2 or SI1 clarity can still look clean. Ratios run from square (1.00 to 1.05) to rectangular (1.30 to 1.50).

A radiant gives you the shape of an emerald with the sparkle of a round.

Who it suits

Choose a radiant cut engagement ring if you want bold, modern lines and a ring that copes with daily life. The cut corners make it very resistant to chipping, so it suits busy hands. It looks superb with tapered baguette side stones or a hidden halo. Its deeper pavilion makes it look slightly smaller face-up than an emerald of the same carat weight.

Typical UK price and what to look for

Radiants usually cost less per carat than rounds. These are indicative prices for IGI-certified stones in E to G colour and VS clarity.

With lab grown loose diamonds UK buyers choose in this cut, ask for a video of the actual stone. Look for even sparkle across the whole face and avoid any stone with a dull, dark centre.

Choosing the right shape for your ring

Shape is the decision everything else follows, so start there. Pick a round for maximum sparkle, an oval or pear for a larger look, an emerald or cushion for a vintage feel, and a radiant for bold lines that cope with daily wear. Whichever you choose, ask to see a video of the actual diamond, not a stock image.

Put your budget into cut quality first, then carat weight. With lab grown diamonds loose, a certified Excellent cut will always look better than a bigger stone that leaks light. Match the setting to the shape, and protect any points or corners with the right claws.

Ready to buy loose lab grown diamonds in the UK with expert help? Talk to the A Star Diamonds team in Hatton Garden and we will help you choose the right stone and design the ring around it, with free lifetime resizing, polishing and cleaning included.