From the bottom of the hoof measure the widest width from side to side and heal to toe. If your horse isn’t comfortable to stand with one leg up to measure the hoof then walk the horse onto a piece of paper and trace the outline of the hoof wall. Once you have measured both the width and length you can see with pad will best suit your horses hoof. The sizes are small 4-3/4 x 5 inches, medium 5-1/4 x 5 ½ inches and large 5-1/2 x 6 inches. If your horse as the exact measurements as the pad then go one size up.