Measure the circumference of the knee at the patella with knee fully extended: X-Small: 12 - 13 inches; Small: 13 - 14.5 inches; Medium: 14.5 - 16 inches; Large: 16 - 17.5 inches; X-Large: 17.5 - 20 inches; XX-Large: 20 - 22.25 inches. LP is recognized as the industry leader in the sports medicine category and in technical protective wear and has been well received by sports medical professionals. Success stories from athletes who have benefited from these innovations inspire us to keep creating high performance protective supports to meet our customers needs.