Shoes should be carefully fitted to your heel as well as your toes. Try on both shoes. Fit new shoes to your largest foot. Most people have one foot larger than the other. Walk around in the shoes to make sure they fit well and feel comfortable.
Sizes vary among shoe brands and styles.
Judge a shoe by how it fits on your foot not by the marked size. When the shoe is on your foot, you should be able to freely wiggle all of your toes. If the shoes feel too tight, don't buy them. Most high heeled-shoes have a pointed, narrow toe box that crowds the toes and forces them into an unnatural triangular shape. As heel height increases, the pressure under the ball of the foot may double, placing greater pressure on the forefoot as it is forced into the pointed toe box.