The Thermoskin 4-Way Elastic Knee Support is anatomically shaped for a comfortable fit. This unique four-way stretch support combines spandex with advanced hosiery technology to provide protection and support for weak and injured knees without continual bunching. It aids in the reduction of swelling and provides temporary pain relief. 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.