0.25ct
4.1mm
Diamond size guide
A carat measures a diamond's weight, not its size. One carat is 0.2 grams, about the weight of a paperclip, split into 100 points. Because carat is weight, two diamonds of the same carat can look different sizes depending on the cut and the shape. This guide shows the common sizes to scale, in millimetres, on the hand and against a coin, so you can picture your piece before it is made.
A diamond next to a 5p coin
A 5p coin is 18.0mm across. Here it is beside round diamonds from a half carat up to five carats at the same scale, so you have something familiar to measure against.
5p coin, 18.0mm
See it on the hand
Drag the slider to see a round diamond grow to scale on the hand, from a quarter carat up to four carats.
1.00ct6.5mm
0.251ct2ct3ct4ct
Sizes to scale
Every diamond below is drawn to the same scale, so you can compare a round, an oval and an emerald cut at each carat weight. The millimetre figure beneath each one is the precise face up measurement.
Round brilliant
0.5ct
5.2mm
0.75ct
5.9mm
1ct
6.5mm
1.5ct
7.4mm
2ct
8.1mm
3ct
9.3mm
Oval brilliant
0.25ct
5.0 x 3.0mm
0.5ct
6.0 x 4.0mm
0.75ct
7.0 x 5.0mm
1ct
7.7 x 5.7mm
1.5ct
8.5 x 6.5mm
2ct
9.0 x 7.0mm
3ct
10.0 x 8.0mm
Emerald step cut
0.25ct
4.5 x 3.5mm
0.5ct
6.0 x 4.0mm
0.75ct
6.5 x 4.5mm
1ct
7.0 x 5.0mm
1.5ct
7.5 x 5.5mm
2ct
8.5 x 6.5mm
3ct
9.5 x 7.0mm
See it worn
The same idea on the ear, at the neck and on the wrist. Drag each slider to grow the stones to scale, from a quiet stud to a statement piece.
Stud on the ear
1.00ct6.5mm
0.25ct3ct
Pendant at the neck
1.00ct6.5mm
0.25ct4ct
Tennis bracelet
5cttotal weight
1ct10ct
Millimetres by carat
| Carat | Round | Oval | Emerald |
|---|---|---|---|
| 0.25ct | |||
| 0.5ct | |||
| 0.75ct | |||
| 1ct | |||
| 1.5ct | |||
| 2ct | |||
| 3ct |
Why two diamonds of the same carat can look different
Carat is weight, so it does not map exactly to the size you see from above. The cut and the shape both change how big a diamond looks for its weight. An elongated shape like an oval or a marquise spreads its weight across the finger and looks larger than a round of the same carat.
Depth matters too. A stone cut too deep hides weight underneath, where you do not see it, so it can look smaller than a well cut stone that weighs the same. This is why we choose and price on the millimetres and the cut, not on the carat alone.
Every diamond below weighs exactly one carat, yet the shape changes how large each one looks.
Round
Princess
Cushion
Emerald
Oval
Marquise
Carat and price
Diamond price does not rise in a straight line with carat. Larger stones are rarer, so the price per carat climbs as the weight goes up, and it jumps at the round numbers the trade calls magic sizes, a half carat, three quarters, one carat and two carats. A stone just under one of these weights can look the same as one just over, for a noticeably lower price.
Because our diamonds are lab grown and we sell direct from Hatton Garden, you get more size and quality for your budget, with no retail markup. Design your piece in the studio to see an indicative price in seconds.
How to make a diamond look bigger
If you want the most presence for the weight, a few choices help. An elongated shape, an oval, a pear or a marquise, reads larger than a round of the same carat. A halo of small diamonds around the centre stone lifts the whole look for little added cost. A slim band and a fine setting make the stone look larger by comparison, and a well cut stone returns more light, which makes it feel brighter and bigger on the hand.
All one carat. The longer shapes spread further across the finger, so they read larger than the round.
Round
Radiant
Oval
Pear
Marquise
Diamond carat questions
What does carat mean?
Carat is the unit for a diamond's weight. One carat is 0.2 grams, about the weight of a paperclip, and it is split into 100 points, so a 0.50ct diamond is fifty points. It measures weight, not size.
How big is a 1 carat diamond?
A well cut 1 carat round diamond measures about 6.5mm across, a little under the width of a pea. An oval or an emerald of the same carat looks longer and narrower. You can see all the common sizes to scale further up this page.
Is a bigger carat always better?
Not always. Carat is only one of the four things that decide how a diamond looks, alongside cut, colour and clarity. A smaller, well cut stone can look brighter and livelier than a larger one that is cut poorly, so it is worth balancing size with cut rather than chasing weight alone.
Which diamond shape looks the biggest?
Elongated shapes look the largest for their weight, because they spread across the finger. Oval, marquise and pear tend to look bigger than a round of the same carat, while a round and an emerald of the same weight usually look a little smaller from above.
What is the difference between carat and karat?
They sound the same but measure different things. Carat, with a c, is the weight of a diamond. Karat, with a k, is the purity of gold, which is why we write 9k or 18k gold. A diamond has a carat weight, a gold band has a karat purity.
How much does a 1 carat lab grown diamond cost?
Lab grown diamonds cost a fraction of mined diamonds of the same size and quality, and because we make to order and sell direct from Hatton Garden there is no retail markup. The exact price depends on the cut, colour and clarity you choose. The quickest way to see a real figure is to design your piece in the studio for an instant indicative price.
What is the most popular carat size?
For engagement rings, most people choose between one and one and a half carats. It is a size with real presence that still sits comfortably for everyday wear. The right size is the one that suits the hand, the setting and the budget.
Drawn to one shared scale for easy comparison, not to your screen's exact size. Use the millimetres as the precise guide. Figures are typical for well cut lab grown diamonds and vary a little stone to stone. Every Luma diamond is independently certified.