January 28th 2022
Round Cut Diamond Size Chart
By Devin Jones
Below is our diamond size chart showing the relationship between carat size, diameter, and surface area for round cut diamonds.
Round
Cushion
Emerald
Oval
Princess
Pear
Radiant
Asscher
Heart
MarquiseRound Cut Diamond Carat Size Chart
| Round Carat Weight | Round MM Size | Surface Area (sq. mm) |
|---|---|---|
| 0.3 ct. | 4.30 | 14.52 |
| 0.4 ct. | 4.73 | 17.59 |
| 0.5 ct. | 5.10 | 20.41 |
| 0.6 ct. | 5.42 | 23.04 |
| 0.7 ct. | 5.70 | 25.53 |
| 0.8 ct. | 5.96 | 27.90 |
| 0.9 ct. | 6.20 | 30.17 |
| 1 ct. | 6.42 | 32.37 |
| 1.1 ct. | 6.63 | 34.49 |
| 1.2 ct. | 6.82 | 36.54 |
| 1.3 ct. | 7.01 | 38.54 |
| 1.4 ct. | 7.18 | 40.49 |
| 1.5 ct. | 7.35 | 42.39 |
| 1.6 ct. | 7.51 | 44.25 |
| 1.7 ct. | 7.66 | 46.07 |
| 1.8 ct. | 7.81 | 47.86 |
| 1.9 ct. | 7.95 | 49.61 |
| 2 ct. | 8.08 | 51.34 |
| 2.1 ct. | 8.22 | 53.03 |
| 2.2 ct. | 8.35 | 54.70 |
| 2.3 ct. | 8.47 | 56.34 |
| 2.4 ct. | 8.59 | 57.96 |
| 2.5 ct. | 8.71 | 59.55 |
| 2.6 ct. | 8.82 | 61.13 |
| 2.7 ct. | 8.93 | 62.68 |
| 2.8 ct. | 9.04 | 64.22 |
| 2.9 ct. | 9.15 | 65.74 |
| 3 ct. | 9.25 | 67.24 |
| 3.1 ct. | 9.35 | 68.72 |
| 3.2 ct. | 9.45 | 70.19 |
| 3.3 ct. | 9.55 | 71.64 |
| 3.4 ct. | 9.65 | 73.08 |
| 3.5 ct. | 9.74 | 74.50 |
| 3.6 ct. | 9.83 | 75.91 |
| 3.7 ct. | 9.92 | 77.31 |
| 3.8 ct. | 10.01 | 78.69 |
| 3.9 ct. | 10.10 | 80.06 |
| 4 ct. | 10.18 | 81.43 |
| 4.1 ct. | 10.27 | 82.77 |
| 4.2 ct. | 10.35 | 84.11 |
| 4.3 ct. | 10.43 | 85.44 |
| 4.4 ct. | 10.51 | 86.76 |
| 4.5 ct. | 10.59 | 88.06 |
| 4.6 ct. | 10.67 | 89.36 |
| 4.7 ct. | 10.74 | 90.65 |
| 4.8 ct. | 10.82 | 91.93 |
| 4.9 ct. | 10.89 | 93.20 |
| 5 ct. | 10.97 | 94.46 |
Round Carat Size vs. Surface Area
The below diamond size chart shows the changing dynamic between an increase in carat size and the respective increase in a round diamond's visual appearance. While carat weight is typically thought of as an indication of a diamond's size (meaning visual appaerance), carat is actually a measure of weight. Diamonds of the same carat size can vary slightly in their visual appearance depending on how they are cut. For instance, a diamond with a deeper cut will appear smaller than a diamond of the same carat weight with a shallower cut.
For our round diamond analysis we averaged the diameters of hundreds of thousands of diamonds from Blue Nile, Enchanted, Whiteflash, and Brian Gavin Diamonds to come up with a simple exponential function (shown on the chart below). Using this formula we can study the corresponding changes in diameter and surface area for a given change in carat weight. Interestingly, as the carat size increases we notice a significant slowing of the surface area. This is because carat weight scales as a measure of volume (mm cube) while surface area scales at a slower rate (mm squared).
