Size guides › Round
Round diamonds
Round diamond size chart
The classic: the most sparkle, and the shape every other is measured against. A round brilliant is cut with 57 or 58 facets arranged to send as much light back to your eye as possible. It's the most popular engagement ring shape, and the one most size charts are really describing.
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Every round size, drawn to scale
From 0.25 to 3 carats, on a millimeter grid. Tap a size for its own guide.
| Carat | Size (mm) | Area | Covers of a size 6 finger |
|---|---|---|---|
| 0.25 ct | 4.05 mm across | 12.9 mm² | 23% |
| 0.5 ct | 5.11 mm across | 20.5 mm² | 29% |
| 0.75 ct | 5.85 mm across | 26.8 mm² | 33% |
| 1 ct | 6.44 mm across | 32.5 mm² | 36% |
| 1.25 ct | 6.93 mm across | 37.7 mm² | 39% |
| 1.5 ct | 7.37 mm across | 42.6 mm² | 42% |
| 2 ct | 8.11 mm across | 51.6 mm² | 46% |
| 2.5 ct | 8.73 mm across | 59.9 mm² | 49% |
| 3 ct | 9.28 mm across | 67.6 mm² | 53% |
Typical proportions. Real stones vary by a few tenths of a millimeter — the certificate gives the exact size.
What to know about round diamonds
Cut quality matters most
GIA gives round brilliants an overall cut grade, from Excellent to Poor, and it's the biggest single factor in how bright the stone looks. Other shapes get no official cut grade, so you judge their proportions instead.
It costs more per carat
Rounds usually cost more per carat than other shapes, partly because more of the rough crystal is cut away to make one.
Four prongs or six
Four prongs show a little more diamond and look slightly square from above; six hold it more securely and keep the outline round.
Why two rounds of the same weight can differ
Carat is weight. All three of these weigh 1 ct, but how deep each is cut changes how wide it looks from above — by more than a third of a millimeter. Compare rounds by millimeters, and look for a good cut grade.
See a round on your own hand
Pick a size, add a photo of your hand, and see it at its real size — with the fit check built in.
Questions
How big is a 1 carat round diamond?
About 6.44 mm across.
What size setting does a round diamond need?
Any common style can be made to fit it: ask for a head the size of the stone — about 6.4 mm for a 1 ct. Ready-made heads in most styles take a round up to about 1.5 ct; above that, choose a setting made to order.