Measure at the mid kneecap, directly on the skin with leg completely straight. Take a soft tape measure and in the center of the knee cap to get your circumfrence measurement.

S	13 to 13  7/8"

M	14 to 14  7/8"

L	15 to 15  7/8"

XL	16 to 16  7/8"

XX	17 to 18  1/8"