Round diamond size chart: carat to mm
By HeyGema™ · Updated
In short
A 1 carat round diamond measures about 6.5 mm face-up.
Carat to mm calculator
About 6.5 x 6.5 mm
An estimate for a well-cut stone. A deep or shallow cut faces up smaller or bigger.
Round diamond size chart (carat to mm)
Face-up length and width of a well-cut round diamond at a length-to-width ratio of 1.00:1.
- 0.25
- Size: 4.1 mm
- 0.33
- Size: 4.5 mm
- 0.5
- Size: 5.1 mm
- 0.75
- Size: 5.9 mm
- 1
- Size: 6.5 mm
- 1.25
- Size: 6.9 mm
- 1.5
- Size: 7.4 mm
- 2
- Size: 8.1 mm
- 2.5
- Size: 8.8 mm
- 3
- Size: 9.3 mm
- 4
- Size: 10.2 mm
- 5
- Size: 11.0 mm
Round diamond on a finger
How much of the finger's width a 1 carat round 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: 43%
- 5
- Finger width: 15.7 mm
- Stone covers: 41%
- 6
- Finger width: 16.5 mm
- Stone covers: 39%
- 7
- Finger width: 17.3 mm
- Stone covers: 37%
- 8
- Finger width: 18.1 mm
- Stone covers: 36%
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.
Questions
A 1 carat round diamond measures about 6.5 mm face-up.
A 2 carat round diamond measures about 8.1 mm face-up.
A 0.5 carat round diamond measures about 5.1 mm face-up.
The chart is for a well-cut stone. A deep cut holds its weight in the depth, so it faces up smaller. Ask for the length, width and depth on the certificate.