http://en.wikipedia.org/wiki/Shoe_size
Some systems also include the width of a foot.
Read from the shoes' tongue label.
There are different methods indicating the width:
The measured width is indicated in millimetres (mm).
This is done with the Mondopoint system.
The measured width is assigned a letter (or combination of
letters), which is taken from a table (indexed to length and width)
or just assigned on an ad-hoc basis:
Examples include (each starting with the narrowest width):
A, B, C, D, E, EE, EEE, EEEE, F, G (typical North American
system)
4A, 3A, 2A, A, B, C, D, E, 2E, 3E, 4E, 5E, 6E (variant North
American)
A, B, C, D, E, F, G (common UK; "medium" is usually F, but varies
by manufacturer—makers Edward Green and Crockett & Jones, among
others, use E instead) N (narrow), M (medium) or R (regular), W
(wide)
The width for which these sizes are suitable can vary significantly
between manufacturers. The A-E width indicators used by most US and
some UK shoe manufacturers are typically based on the width of the
foot, and common step sizes are 3/16 of an inch.