Foot length versus shoe length
The length of a foot is commonly defined as the horizontal distance between two parallel lines that are perpendicular to the foot and in contact with the most prominent toe and the most prominent part of the heel. Foot length is measured with the subject standing barefoot and the weight of the body equally distributed on both feet.
The size of the left and right foot is often slightly different for many people. In order to choose a shoe size, both feet should be measured and then the shoe size should be chosen based on the larger foot.
Each shoe is suitable for a small interval of foot lengths. The length of the inner cavity of a shoe must typically be 15-20 mm longer than the length of the foot, but this relation varies between different types of shoes.
There are three characteristic lengths that a shoe-size system can refer to:
All these measures differ substantially from each other for the same shoe.
Traditional shoe sizes by country
Warning: Most of the shoe-size systems listed in this section are not formally standardized. The exact relationship between a labelled shoe size and the interval of foot lengths for which that shoe is suitable can vary substantially between different manufacturers. The following descriptions may only approximate the exact sizing systems used by individual manufacturers. One source of discrepancy occurs when a shoe manufactured according to one shoe-size system is labeled in another system.
In France, Germany, and most other European countries, the traditional shoe size is the length of the last, measured in Paris points. For shoe types where the last is 20 mm longer than the foot for which the shoe will fit:
The United Kingdom and Australia determine shoe sizes by the length of the last, measured in barleycorns, minus a constant. The UK and Australia use different constants for women's shoes, though they use the same constant for men's.
United States and Canada
Shoe size in the United States and Canada is based on the length of the last, measured in barleycorns, minus a constant. This constant differs for shoes intended for men, women and children.
Women's sizes are almost always determined with the "common" scale, in which women's sizes are equal to men's sizes plus 1.5 (for example, a men's 10.5 is a women's 12). In the less popular scale, known as the "standard" or "FIA" (Footwear Industries of America) scale, women's sizes are men's sizes plus 1 (so a men's 10.5 is a women's 11.5).
Kid's sizes are equal to men's sizes plus 12.33. Thus girl's and boy's sizes do not differ, even though men's and women's do.
Width or girth designators
Some manufacturers offer shoes of different width for the same foot length. Such shoes are then also labelled according to the width or girth of the widest part of the foot (typically measured directly behind the toes with the subject standing on both feet and wearing socks or hose).
In the Mondopoint system, the shoe size label can state in addition to the length also the width of the mean foot for which the shoe is suitable, both measured in millimetres.
A number of other ad-hoc notations for width or girth are also used. Examples include (each starting with the narrowest width):
None of these designations are formally standardized. The exact foot width for which these sizes are suitable can vary significantly between manufacturers. The A-E width indicators used by some US and UK shoe manufacturers are typically based on the width of the foot, and common step sizes are 1/4 inch (6 mm) or 3/16 inch (5 mm).