Children from 7 years and ladies should choose size M, men size L.
In case of doubt, you should choose the larger version, as the mask can be fitted exactly thanks to the individually adjustable ear loops.
Dimensions of the face mask Pro:
S: 13 x 16 x 0,5 cm
M: 14 x 17 x 0,5 cm
L: 15 x 18 x 0,5 cm