Radiant cut diamond size chart: carat to mm
By HeyGema™ · Updated
In short
A 1 carat radiant cut diamond measures about 6.5 x 5.0 mm face-up. It faces up 2% smaller than a 1 carat round diamond.
Carat to mm calculator
About 6.5 x 5.0 mm
An estimate for a well-cut stone. A deep or shallow cut faces up smaller or bigger.
Radiant cut diamond size chart (carat to mm)
Face-up length and width of a well-cut radiant cut diamond at a length-to-width ratio of 1.30:1.
- 0.25
- Size: 4.1 x 3.1 mm
- 0.33
- Size: 4.5 x 3.5 mm
- 0.5
- Size: 5.2 x 4.0 mm
- 0.75
- Size: 5.9 x 4.5 mm
- 1
- Size: 6.5 x 5.0 mm
- 1.25
- Size: 7.0 x 5.4 mm
- 1.5
- Size: 7.4 x 5.7 mm
- 2
- Size: 8.2 x 6.3 mm
- 2.5
- Size: 8.8 x 6.8 mm
- 3
- Size: 9.4 x 7.2 mm
- 4
- Size: 10.3 x 7.9 mm
- 5
- Size: 11.1 x 8.5 mm
Size by length-to-width ratio
The same weight can be long and thin or short and wide. These are 1 carat sizes at each ratio.
- 1.00:1
- 1 ct: 5.7 x 5.7 mm
- 1.15:1
- 1 ct: 6.1 x 5.3 mm
- 1.30:1
- 1 ct: 6.5 x 5.0 mm
- 1.40:1
- 1 ct: 6.7 x 4.8 mm
Radiant cut diamond on a finger
How much of the finger's width a 1 carat radiant cut diamond covers, by US ring size. Finger width is taken as the ring's inside diameter. The more of the finger it covers, the bigger it looks.
- 4
- Finger width: 14.9 mm
- Stone covers: 34%
- 5
- Finger width: 15.7 mm
- Stone covers: 32%
- 6
- Finger width: 16.5 mm
- Stone covers: 30%
- 7
- Finger width: 17.3 mm
- Stone covers: 29%
- 8
- Finger width: 18.1 mm
- Stone covers: 28%
Check the real size
A chart on a screen is hard to picture. Hold a ruler or a bank card (85.6 x 54 mm) up to the screen, or ask your jeweler for a cubic zirconia of the same size to try on.