The Thermoskin Elastic Knee Stabilizer Support is anatomically designed for comfort and fit. It provides even compression and support for weak and injured knees, while minimizing bunching. The side stabilizers provide increased medial and lateral support to weak and injured knees. Knee Sizing Guide: Measure the circumference just below the knee cap. Small 12 - 13 1/2 inches. Medium 13 1/2 - 15. Large 15 - 16 1/2. X-Large 16 1/2 - 18 inches. If in doubt on Thermoskin sizing it is generally best to select the larger size.