How are urinary catheters sized?

I'm often asked how are urinary catheters sized and what do the different colour funnels on the catheters mean?

Indwelling and intermittent catheters are sized using a number system and maybe denoted by Charriere (Ch), French gauge (Fg) or French (Fr).

1 Ch, Fg or Fr is equal to 1/3rd of a millimetre therefore a size 12ch would be 4 mm in diameter, measuring the outside width of the catheter tubing.

Each Ch, Fg and Fr is also given a colour coding so identification can be distinguished at a glance.

This sizing is universal, on indwelling foley catheters the size should be written somewhere on the catheter near where it connects to the drainage bag.

Intermittent catheters can be coded by having a coloured funnel. Wymedical catheters and dilators can be differentiated by the different coloured funnels.

Catheter Sizing

Catheter Funnel Colours