The relative size of a Foley catheter is described using French units (F). Alternatively, the size of a 10 F catheter might be expressed as 10 Ch (Charriere units – named after a 19th century French scientific instrument maker, Joseph-Frédéric-Benoît Charrière). The most common sizes are 10 F to 28 F. 1 F is equivalent to 0.33 mm = .013" = 1/77" of diameter. Foley catheters are usually color coded by size with a solid color band at the external end of the balloon inflation tube, allowing for easy identification of the size. Note: Colors for French sizes 5, 6, 8, 10 may vary significantly if intended for pediatric patients. Color for French size 26 may also be pink instead of black.
https://en.wikipedia.org/wiki/Foley_catheter
Based on this paragraph, what is the diameter of a 10 F Foley catheter in mm?
According to this paragraph, the diameter of a 1 F catheter is 1/77mm so the diameter of a 10 F catheter is 10/77mm.