General sizes are (wide/large):

XS Women ............ 16"/20"
S Women ........... 16.5"/21"
M Women ............. 18"/23"
XSMen/LWomen . 18.5"/25"
S Men ................. 19.5"/28"
M Men ................. 21"/28.5"
L Men ................... 22"/29"
XL Men ................ 23.5"/30"
S (fit.) Women ... 16"/21.5"
M (fit.) Women ..... 17"/22"
L (fit.) Women ...... 18"/23"

XS Infant ...... 1-2 Years
S Infant ........ 3-4 Years
M Infant ....... 5-6 Years
L Infant ........ 7-8 Years
XL Infant ...... 9-10 Years