Found it:
http://www2.pocsports.com/products/sizeguide.asp?season=Ski

circumference calf
S 30-34 cm 11,8-13,4 "
M 34-38 cm 13,4-15 "
L 38-42 cm 15-16,5 "

circumference 10 cm above centre knee cap
S 37-41 cm 14,6-16,1 "
M 41-45 cm 16,1-17,7 "
L 45-49 cm 17,7-19,3 "