To determine the size needed, place the foot at a 90-degree angle in relation to the lower leg, and measure the circumference around the heel and instep of the foot. Size 1 fits 10-1/2-12/1/4 inches, size 2 fits 12-1/4-13-1/8 inches, and size 3 fits 13-1/8 to 15-3/4 inches. See the instruction sheet for more information about measuring.