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Carat is a unit of weight, not size: one carat is 0.2 gram. How large a diamond looks depends on its shape and its cut proportions, so two 1 carat diamonds can measure differently across. This chart gives the typical face-up millimetre size for each carat weight in the common shapes, based on well-cut stones. Use it to picture a diamond before buying, to compare shapes at the same weight, and to understand why an oval or pear looks bigger than a round of the same carat. Every Ivana Jewels product page lists the actual measurements from the stone's IGI or SGL certificate.
Round brilliant: carat to mm
| Carat | Diameter (mm) | Carat | Diameter (mm) |
|---|---|---|---|
| 0.25 | 4.1 | 1.50 | 7.4 |
| 0.30 | 4.3 | 1.75 | 7.8 |
| 0.40 | 4.8 | 2.00 | 8.1 |
| 0.50 | 5.1 | 2.50 | 8.8 |
| 0.70 | 5.7 | 3.00 | 9.3 |
| 0.75 | 5.8 | 4.00 | 10.2 |
| 0.90 | 6.2 | 5.00 | 11.0 |
| 1.00 | 6.5 | 6.00 | 11.7 |
| 1.25 | 6.9 | 10.00 | 14.0 |
Doubling the carat weight does not double the diameter: a 2 carat round is about 25% wider than a 1 carat, because weight is spread through depth as well as width.
Fancy shapes: typical size at 1 and 2 carat
| Shape | 1 carat (mm) | 2 carat (mm) | Looks larger or smaller than a round? |
|---|---|---|---|
| Round | 6.5 | 8.1 | Baseline |
| Oval | 7.7 x 5.7 | 10.0 x 7.5 | Larger |
| Pear | 8.5 x 5.5 | 11.0 x 7.0 | Larger |
| Marquise | 10.0 x 5.0 | 13.0 x 6.5 | Largest |
| Emerald | 6.7 x 4.8 | 8.5 x 6.0 | Similar |
| Cushion | 5.9 | 7.5 | Slightly smaller |
| Princess | 5.5 | 7.0 | Smaller across, wider corner to corner |
| Heart | 6.5 | 8.2 | Similar |
| Radiant | 6.3 x 5.5 | 8.0 x 7.0 | Slightly smaller |
Figures are for typical proportions; a shallow stone measures larger and a deep stone smaller at the same weight. Browse by shape: oval, pear, emerald cut, cushion, princess, marquise.
How size reads on the hand
A 0.5 carat round (5.1 mm) reads as a clear everyday diamond. 1 carat (6.5 mm) is the benchmark engagement size and is visible across a table. 1.5 carat (7.4 mm) is the first step most people notice at a glance. 2 carat (8.1 mm) is a statement; 3 carat (9.3 mm) spans much of a slim finger. Finger size matters: the same 1 carat stone looks larger on a size 10 finger than on a size 16. Elongated shapes (oval, pear, marquise) cover more finger and make it look longer. See the live 1 carat, 2 carat and 3 carat ring collections.
Stud earrings: per-earring size
| Per earring | Round diameter (mm) | How it reads |
|---|---|---|
| 0.25 carat | 4.1 | Subtle, everyday |
| 0.50 carat | 5.1 | Classic daily stud, the most gifted size |
| 0.75 carat | 5.8 | Visible without being large |
| 1.00 carat | 6.5 | Clearly visible from a distance |
| 2.00 carat | 8.1 | Statement |
Studs are quoted either "each" or "total"; 1 carat each is two 6.5 mm stones, 1 carat total is two 5.1 mm stones. Ivana Jewels titles say "each" where it applies. See 1 carat studs.
Pendants
A pendant is viewed from further away than a ring, so the same carat weight reads slightly smaller. 0.5 carat (5.1 mm) is the everyday solitaire pendant; 1 carat (6.5 mm) is the most gifted; elongated shapes suit pendants well because they follow the line of the neck.
Frequently asked questions
How big is a 1 carat diamond in mm?
About 6.5 mm across for a round brilliant; 7.7 x 5.7 mm for an oval; 8.5 x 5.5 mm for a pear.
Does a 2 carat diamond look twice as big as 1 carat?
No. It is twice the weight but about 25% wider (8.1 mm vs 6.5 mm). The difference is clear on the hand but not double.
Which shape looks biggest per carat?
Marquise, then pear and oval. Round is in the middle; cushion, princess and radiant carry more weight in depth and look slightly smaller across.
Does carat size work the same for lab grown diamonds?
Yes. Carat weight and millimetre size are identical for lab grown and mined diamonds of the same cut. The difference is price, which is why 2 and 3 carat lab grown rings are common where 2 carat natural rings are not.
Where do I find the exact size of a specific diamond?
On its IGI or SGL certificate, in the measurements line (length x width x depth). Ivana Jewels product pages show these for each stone.
