Hello, you should place your foot on the paper. The heel of the foot should coincide with the back edge of the paper. A thick book, box, or the wall of your house can make a back border. You can place the ruler on the tip of the longest finger and draw the mark line from the inside of the ruler. The part on the left edge of the paper, up to the fingertip, gives the correct foot size in CM. Size measurement chart; 36-23 cm, 37-23.6 cm, 38-24.3 cm, 39-25 cm, 40-25.6 cm, 41-26.3 cm, 42-27 cm, 43-27.6 cm, 44-28.3 cm, 45-29 cm, 46-29.6 cm, 47-30.3 cm.