Catheters come in different shapes and sizes. The size of the catheter will differ depending on your specific needs and requirements.
The diameter of a catheter is measured in “French Units” or “Fr”. A single French Unit (1 FR) is 0.33mm.
1 FR = 0.33mm = .013” (or 1/77”)
Here is a sizing scale measuring the outside diameter for catheters in French Units:
| FR | 12 | 14 | 16 | 18 | 20 | 22 | 24 | 26 | 28 |
| mm | 4 | 4.7 | 5.3 | 6 | 6.7 | 7.4 | 8 | 8.7 | 9.4 |
| inch | 0.16 | 0.185 | 0.21 | 0.24 | 0.265 | 0.295 | 0.32 | 0.345 | 0.375 |
| FR | 30 | 32 | 34 | 36 | 38 | 40 | 42 | 48 |
| mm | 10 | 10.7 | 11.3 | 12 | 12.7 | 13.4 | 14 | 16 |
| inch | 0.4 | 0.425 | 0.455 | 0.48 | 0.5 | 0.53 | 0.55 | 0.64 |
Foley Catheters also have a measurement for their balloon capacity. This measurement is in cubic centimeters and translates directly into milliliters.
1 CC = 1 mL
