Interactive diamond size chart showing mm to carat conversion for every diamond shape. Visual comparison tool with face-up dimensions from 0.8mm melee to 11mm (5 carat).
- Covers all major shapes: Round, Oval, Cushion, Emerald, Pear, Princess, Marquise, Radiant, Asscher, Heart
- Shows actual mm dimensions for each carat weight
- Interactive shape selector and visual size comparison
- Includes FAQ on diamond measurement, melee sizes, and setting impact
- Free to use, no signup required
Round Brilliant Diamond Size Chart
Actual mm dimensions for round brilliant diamonds at every carat weight.
Round
Oval
Cushion
Princess
Emerald
Pear
Radiant
Marquise
Asscher
Heart
Trilliant
Baguette
Old Mine
Rose CutRound Brilliant Sizes
Shape guide →| MM Size | Carat Weight |
|---|---|
| 0.8 mm | 0.002 ct |
| 0.9 mm | 0.004 ct |
| 1 mm | 0.005 ct |
| 1.1 mm | 0.0068 ct |
| 1.2 mm | 0.0085 ct |
| 1.3 mm | 0.01 ct |
| 1.4 mm | 0.012 ct |
| 1.5 mm | 0.015 ct |
| 1.6 mm | 0.018 ct |
| 1.7 mm | 0.019 ct |
| 1.8 mm | 0.025 ct |
| 1.9 mm | 0.028 ct |
| 2 mm | 0.03 ct |
| 2.1 mm | 0.035 ct |
| 2.2 mm | 0.04 ct |
| 2.3 mm | 0.045 ct |
| 2.4 mm | 0.055 ct |
| 2.5 mm | 0.06 ct |
| 2.6 mm | 0.065 ct |
| 2.7 mm | 0.075 ct |
| 2.8 mm | 0.085 ct |
| 2.9 mm | 0.093 ct |
| 3 mm | 0.1 ct |
| 3.1 mm | 0.11 ct |
| 3.2 mm | 0.13 ct |
| 3.3 mm | 0.14 ct |
| 3.4 mm | 0.15 ct |
| 3.5 mm | 0.17 ct |
| 3.6 mm | 0.19 ct |
| 3.7 mm | 0.2 ct |
| 3.8 mm | 0.22 ct |
| 3.9 mm | 0.23 ct |
| MM Size | Carat Weight |
|---|---|
| 4 mm | 0.25 ct |
| 4.1 mm | 0.26 ct |
| 4.2 mm | 0.28 ct |
| 4.3 mm | 0.3 ct |
| 4.4 mm | 0.33 ct |
| 4.5 mm | 0.36 ct |
| 4.6 mm | 0.4 ct |
| 4.7 mm | 0.43 ct |
| 4.8 mm | 0.45 ct |
| 4.9 mm | 0.48 ct |
| 5 mm | 0.5 ct |
| 5.1 mm | 0.53 ct |
| 5.2 mm | 0.56 ct |
| 5.3 mm | 0.58 ct |
| 5.4 mm | 0.63 ct |
| 5.5 mm | 0.66 ct |
| 5.6 mm | 0.7 ct |
| 5.8 mm | 0.75 ct |
| 6 mm | 0.84 ct |
| 6.3 mm | 0.93 ct |
| 6.5 mm | 1 ct |
| 6.8 mm | 1.25 ct |
| 7 mm | 1.3 ct |
| 7.3 mm | 1.5 ct |
| 7.8 mm | 1.75 ct |
| 8 mm | 2 ct |
| 8.7 mm | 2.5 ct |
| 9.1 mm | 3 ct |
| 9.8 mm | 3.5 ct |
| 10.3 mm | 4 ct |
| 11 mm | 5 ct |
Approximate dimensions for well-cut stones. Always verify against the grading report.
How mm to carat conversion works
Carat measures weight, not size. A 1 carat round diamond typically measures 6.5mm across, but that number shifts based on how the stone is cut. Shallow stones spread wider. Deep stones look smaller face-up.
For round diamonds, the measurement is a single diameter. For fancy shapes (oval, pear, emerald, etc.), it's length x width. All numbers here assume well-cut stones with industry-standard proportions.
When buying, always check the actual mm dimensions on the grading report. Two 1-carat rounds can differ by half a millimeter, and that shows on the finger.
Common questions
Diamond size is measured in millimeters (mm) using face-up dimensions. That's what you see looking straight down at the stone. Carat is weight (1 carat = 200 milligrams), not size. Two stones of equal carat weight can measure differently depending on how they're cut.
Yes. A shallow-cut diamond spreads weight across the top, so it looks bigger face-up. A deep-cut stone hides weight underneath, appearing smaller. This is exactly why mm measurements matter more than carat weight alone when you're comparing stones.
Marquise and pear shapes have the largest face-up area per carat, followed by oval. Round diamonds look smallest per carat because they carry more weight in depth. If maximizing visual size matters to you, go elongated.
These conversions are based on industry-standard measurements for well-cut stones with ideal proportions. The data matches what suppliers like Nivoda and GIA use. Actual dimensions vary by cut quality, depth percentage, and girdle thickness.
Significantly. Halo settings add perceived size by surrounding the center stone with melee. Bezel settings cover the girdle, making stones look slightly smaller. Thin bands make the center stone pop by contrast. A 0.9ct in a halo can look bigger than a 1.2ct solitaire.
Anything under 0.20 carats (roughly 3.8mm diameter for round). The trade breaks it down further: 'stars' are 1.2-1.7mm, 'fulls' are 1.7-2.6mm, and 'pointers' are 2.7-3.8mm. These are the small accent stones you see in pavé and halo settings.