If you have found a cushion cut diamond described as 7mm and you are trying to work out how big that really is, here is the direct answer: a square cushion cut measuring roughly 7mm across usually weighs around 2 carats, give or take. A sensible working range is 1.8 to 2.2 carats.

That “give or take” matters, and this guide explains why two stones can both measure 7mm and still differ in weight by a noticeable amount.

First, what the two measurements actually mean

Millimetres (mm) describe the physical size of the stone across the top, which is what you see when the ring is on the hand.

Carat (ct) is a unit of weight, not size. One carat is 0.2 grams. A great deal of a diamond’s weight can sit below the surface, hidden inside the setting, where nobody sees it.

This is why two rings can look identical on the finger while one is described as heavier. When people ask “how many carats is a 7mm cushion”, they are really asking how the visible size translates into the number on the certificate.

The cushion cut, briefly explained

A cushion cut is a square or slightly rectangular stone with rounded corners and softly curved sides, so it looks a little like a pillow. It is an old shape, and it has a warmer, more rounded sparkle than a modern round brilliant.

Cushions come in two broad families:

• Square cushions, where the length and width are almost equal. A 7mm square cushion is close to 7mm x 7mm.
• Elongated cushions, which are noticeably longer than they are wide. A “7mm” elongated cushion might be 7mm x 5.5mm, and that stone will weigh less than a square one.

So before comparing, check whether the seller has quoted one measurement or two.

Approximate size to weight guide for cushion cut diamonds

The figures below are typical approximations for well-proportioned square cushions. They are guidance, not a guarantee. Always go by the actual measurements on the certificate.

Approximate size (square cushion)	Typical carat weight
4.5mm	Around 0.50ct
5.0mm	Around 0.70ct
5.5mm	Around 1.00ct
6.0mm	Around 1.25ct
6.5mm	Around 1.50ct
7.0mm	Around 2.00ct
7.5mm	Around 2.50ct

Notice how quickly weight climbs. Going from 6.5mm to 7mm looks like a small step across the top, but adds roughly half a carat, because weight increases in three dimensions while width increases in only one.

Why two 7mm cushions can weigh different amounts

Depth

Depth is how far the stone goes from the flat top down to the point underneath. A deep-cut stone hides weight below the setting. Two 7mm cushions, one shallow and one deep, can differ by 0.3ct or more with no visible difference on the hand. Shallower is usually better value, as long as it is not so shallow that the stone loses sparkle.

Shape family

A square cushion at 7mm x 7mm carries far more weight than an elongated cushion at 7mm x 5.5mm. Always compare like with like.

Corner and girdle thickness

The girdle is the thin band around the widest point of the stone. A thick girdle adds weight that you cannot see. It also protects the edges, so a medium girdle is the sensible middle ground.

How a 7mm cushion looks in real life

A 7mm cushion is a substantial ring. On an average UK finger size (around L to N), it covers a good portion of the finger width and is impossible to miss. It is larger than most people picture when they say “two carats”, because the rounded corners fill the space that a square princess cut would leave sharp.

If that sounds like more than you want, a 5.5mm to 6mm cushion, roughly 1 to 1.25 carats, is the size most of our customers settle on. It still reads clearly as a diamond ring across a table but sits comfortably under gloves and jumper sleeves.

Cushion rings we make, and what they cost

Our cushion cut pieces are hand-made in solid gold, platinum or sterling silver with lab-grown diamonds, and the centre stone comes with a free IGI certificate. Prices correct at the time of writing.

Ring	Description	Price
Bezel Cushion Cut Engagement Ring in Platinum	Stone held in a rim of metal, very secure	£904
Three Stone Cushion Cut Engagement Ring	Centre cushion with two side stones	£957
Solitaire Cushion Cut Wedding Band in Sterling Silver	Slim band, single cushion stone	£904

We hold three cushion designs in the ready-made collection, so if you want a 7mm centre stone specifically, that is a bespoke piece. There is no extra design cost for bespoke work with us: you pay for the stone and the metal, and we design it with you at no charge.

Browse the wider cushion cut collection or all engagement rings to compare shapes side by side.

A practical way to choose your size

1. Cut a paper circle at the mm size you are considering and tape it to your finger. It feels silly and it works.
2. Decide whether you want the ring to sit flat under gloves. Bezel settings, where a rim of metal wraps the stone, sit lower than tall claw settings.
3. Ask for the mm measurements, not just the carat weight. Two sellers quoting “2 carat” can be selling visibly different sizes.
4. Check the certificate. Ours are IGI and free on centre stones, and they list the measurements in millimetres.

Frequently asked questions

How many carats is a 7mm cushion cut diamond?

Around 2 carats for a well-proportioned square cushion, with a realistic range of roughly 1.8 to 2.2 carats depending on depth and girdle thickness. An elongated 7mm x 5.5mm cushion weighs considerably less, closer to 1.2 to 1.4 carats.

Is a 7mm cushion the same size as a 7mm round?

They cover a similar width, but the cushion has more surface area because the corners are filled in rather than curved away. A 7mm round is roughly 1.25ct; a 7mm square cushion is roughly 2ct.

Does a cushion cut look bigger than its carat weight?

Compared with a round of the same weight, a cushion usually looks slightly smaller face-up, because cushions are often cut deeper. Elongated cushions look larger than square ones of the same weight. This is exactly why measurements in millimetres are more useful than carat weight when you are judging size.

Do you sell 7mm cushion cut lab-grown diamonds?

Not as a ready-made ring at present. We can source one and build the ring around it as a bespoke commission, at no extra design cost. Send us the size and style you have in mind and we will quote honestly.

Will a bigger stone need a stronger setting?

Larger stones sit higher and catch more, so yes, the setting matters more. A bezel setting or a four-claw setting with slightly heavier claws is the usual answer, and we will talk it through before making anything.

In short

7mm cushion is about 2 carats, but always ask for both measurements and the depth before you compare prices. Everything we make is hand-made in solid gold, platinum or silver at our North Harrow workshop in London, with free insured UK delivery and 30-day returns, so you can see the size on your own hand before deciding.

More guides on this topic

• What Are the Types of Diamond Cuts? A Plain-English Guide