What is Shoe size?

A shoe size is an indication of the fitting size of a shoe for a person.

There are a number of different shoe-size systems used worldwide. While all shoe sizes use a number to indicate the length of the shoe, they differ in exactly what they measure, what unit of measurement they use, and where the size 0 is positioned. Some systems also indicate the shoe width, sometimes also as a number, but in many cases by one or more letters. Some regions use different shoe-size systems for different types of shoes. This article sets out several complexities in the definition of shoe sizes. In practice, shoes are often tried on for both size and fit before they are purchased.