Pick the recumbent size that matches your X-Seam Measurement. To measure your X-Seam, sit flat on the floor with your back against the wall and measure from the wall to the bottom of your feet. Point your toes straight up, so that your feet are perpendicular to the floor. Be sure your back is against the wall and your legs are flat on the floor. If you're close to either end of the X-Seam range, just ask us and we'll help you choose the proper size.