The measurement is taken directly where the belt is worn. While standing, lift your leg up and feel where the crease near your hips forms. This area is where the belt is worn and the area that should be measured to ensure the correct size is chosen. For more information on positioning and placement of the Serola Sacroiliac Belt, please see our instructional video at https://www.youtube.com/watch?v=YIdOLp5ByWU. If you are using the belt during pregnancy, please see our specific instructional video for pregnancy found at https://www.youtube.com/watch?v=IuOEOOtwIyg