The American system developed in the 1800s, with sizing based on 1/3-inch intervals for whole sizes. In the European Union, your shoe size is the length of your foot plus two centimeters for comfort.

Usually, men's shoes run 1-1.5 sizes bigger than women's. So if you have your eye on a pair of Chelsea boots from the men's department, snag a size 7 if you're an 8.5 in women's.