To determine the size needed measure the circumference of your ankle.
XS: fits 8.25 - 8.75 inch circumference
S: fits 8.75 - 9.5 inch circumference
M: fits 9.5 - 10 inch circumference
L: fits 10 - 10.5 inch circumference
XL: fits 10.5 - 11 inch circumference
XXL: fits 11 - 11.5 inch circumference