Carat to Millimetre Conversion Chart

Use this guide to compare a diamond's carat weight to its approximate top dimensions. Please note this is only a rough guide as the weight of the stone will vary depending upon its depth.

In the case of brilliant cut diamonds, the millimetre value refers to the stone's diameter. For princess cut diamonds, the millimetre value means that dimension square.

 

BRILLIANT CUT PRINCESS CUT MARQUISE CUT OVAL CUT PEAR CUT EMERALD CUT
0.06-0.08cts = 2.5mm 0.06-0.08cts = 2.1-2.2mm 0.07ct = 4X2mm 0.15-0.18ct = 4X3mm 0.15-0.18ct = 4.5X3mm 0.25ct = 4X3mm
0.10-0.12cts = 3mm 0.10-0.12cts = 2.5-2.7mm 0.15ct = 5X2mm 0.25ct = 5X3mm 0.25ct = 5X3.5mm 0.35ct = 5X3mm
0.16-0.18cts = 3.5mm 0.16-0.18cts = 3mm 0.20ct = 5X3mm 0.40ct = 5X4mm 0.35ct = 5.75X4mm 0.40ct = 5X3.5mm
0.20-0.22cts = 3.8mm 0.20-0.22cts = 3.2-3.3mm 0.25ct = 6X3mm 0.50ct = 6X4.5mm 0.40ct = 6X4mm 0.50ct = 5X4mm
0.24-0.26cts = 4mm 0.24-0.26cts = 3.4-3.5mm 0.35ct = 6.5X3.5mm 0.65ct = 6.5X4.5mm 0.50ct = 6.5X4.5mm 0.60ct = 6X3mm
0.27-0.29cts = 4.2mm 0.27-0.29cts = 3.5mm 0.35ct = 7X3mm 0.75ct = 7X5mm 0.75ct = 7X5mm 0.70ct = 6X4mm
0.30-0.35cts = 4.5mm 0.30-0.35cts = 3.8-3.9mm 0.40ct = 6.5X4mm 1.00ct = 7.5X5.5mm 1.00ct = 8X5mm 0.80ct = 6.5X4.5mm
0.36-0.38cts = 4.6mm 0.36-0.38cts = 3.8-3.9mm 0.50ct = 7X4.5mm 1.25ct = 8X6mm 1.50ct = 9X6mm 0.95ct = 7X4mm
0.39-0.43cts = 4.7-4.8mm 0.39-0.43cts = 3.9-4.1mm 0.70ct = 8X5mm 1.50ct = 8.5X6.5mm   1.00ct = 7X5mm
0.44-0.47cts = 4.8-4.9mm 0.44-0.47cts = 4.1-4.3mm 0.70ct = 9X4mm 1.75ct = 9X6mm   1.25ct = 7.5X5.5mm
 0.48-0.52cts = 5mm  0.48-0.52cts = 4.3-4.5mm  0.75ct = 9X4.5mm  2.00ct = 9X6mm    1.50ct = 8X5mm
 0.53-0.59ctsct = 5.2mm  0.53-0.59ctsct = 4.6mm 0.80ct = 9X5mm       2.00ct = 8.5X6.5mm
 0.60-0.62cts = 5.3-5.4mm  0.60-0.62cts = 4.7mm  1.00ct = 9X6mm      2.25ct = 9X6mm
 0.63-0.68ctsct = 5.5-5.6mm  0.63-0.68ctsct = 4.8mm        2.50ct = 9X7mm
 0.69-0.74cts = 5.6-5.8mm  0.69-0.74cts = 4.8-4.9mm        
 0.75-0.80cts = 5.9-6mm  0.75-0.80cts = 4.9-5mm        
 0.90-0.92cts = 6.2-6.3mm  0.90-0.92cts = 5.1-5.2mm        
 0.93cts-0.99cts = 6.3-6.4mm  0.93cts-0.99cts = 5.2-5.3mm        
1.0cts-1.05cts = 6.4-6.5mm 1.0cts-1.05cts = 5.3-5.5mm        
Approx 1.1cts = 6.6mm Approx 1.1cts = 5.8mm        
Approx 1.25cts = 6.8-6.9mm Approx 1.25cts = 6mm        
Approx 1.3cts = 7mm Approx 1.3cts = 6.1mm        
Approx 1.4cts = 7.2-7.3mm Approx 1.4cts = 6.2mm        
Approx 1.5cts = 7.5mm Approx 1.5cts = 6.4mm        
Approx 1.75cts = 7.7-7.8mm Approx 1.75cts = 6.6-6.8mm        
Approx 2cts = 8-8.2mm Approx 2cts = 7mm