Small
(Men's < 5 1/2, Women's < 7)

Medium
(Men's 5 1/2 to 8, Women's 7 to 9 1/2)

Large
(Men's 8 to 11, Women's 9 1/2 to 12 1/2)

Extra Large
(Men's 11 and up, Women's 12 1/2 and up)