Carats to millimeters across
Type a value in ct to get it in mm instantly.
5.122mm
That's about the same as a half-carat diamond. A well-cut round brilliant 5.122 mm across weighs about 0.5 ct.
Convert the other way: mm to ct
What it means
How big is that stone?
For well-cut round brilliants. Deep stones weigh more for their spread and shallow ones less; other shapes and gems differ.
The math
How to convert ct to mm
For a round brilliant: carats ≈ 0.00372 × diameter³ (diameter in mm), so diameter ≈ ∛(carats ÷ 0.00372).
Example: 0.5 ct = 5.12243 mm.
Every unit
That diamond in every unit
Tables
ct to mm conversion table
| ct | mm |
|---|---|
| 0.1 ct | 2.99561 mm |
| 0.2 ct | 3.77424 mm |
| 0.25 ct | 4.06567 mm |
| 0.3 ct | 4.32042 mm |
| 0.4 ct | 4.75524 mm |
| 0.5 ct | 5.12243 mm |
| 0.75 ct | 5.86371 mm |
| 1 ct | 6.45385 mm |
| 1.25 ct | 6.9522 mm |
| 1.5 ct | 7.38782 mm |
| 2 ct | 8.13134 mm |
| 2.5 ct | 8.75923 mm |
| 3 ct | 9.30807 mm |
| 4 ct | 10.2449 mm |
| 5 ct | 11.0359 mm |
mm to ct conversion table
| mm | ct |
|---|---|
| 3 mm | 0.10044 ct |
| 3.77 mm | 0.199327 ct |
| 4.07 mm | 0.250799 ct |
| 4.32 mm | 0.299912 ct |
| 4.76 mm | 0.401203 ct |
| 5.12 mm | 0.49929 ct |
| 5.86 mm | 0.748576 ct |
| 6.45 mm | 0.99821 ct |
| 6.95 mm | 1.24881 ct |
| 7.39 mm | 1.50133 ct |
| 8.13 mm | 1.99901 ct |
| 8.76 mm | 2.50066 ct |
| 9.31 mm | 3.00187 ct |
| 10.2 mm | 3.94769 ct |
| 11 mm | 4.95132 ct |
Quick answers
Quick answers
- How many mm is 1 ct?
- 1 ct is 6.45385 mm.
- How many mm is 10 ct?
- 10 ct is 13.9044 mm.
- How many mm is 0.5 ct?
- 0.5 ct is 5.12243 mm.
The units
About these units
Carats (ct)
The weight of the stone: 0.2 g per carat.
Millimeters across (mm)
The diameter of a round brilliant, girdle to girdle.
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