In Spain, France, Italy and Germany and most other European countries, shoe size is calculated according to the Continental European system, which uses Paris points (2/3 of a centimeter), where shoe size = 3/2 x foot length (in centimeters) + 1.5 centimeters. This system doesn’t take into account the width of the foot. American shoe sizes are based on the length and width of the foot in inches.
European shoe sizes are commonly expressed as much larger numbers – 17 (105 millimeters) - 47 ½ (315 millimeters) than American sizes. Traditionally, European shoes come in only medium widths because they are based on templates derived from measuring a specific individual’s feet for specific styles of shoes. Called “last” lengths, these foot-shaped templates don’t specify manufacturing tolerances or foot sizes a shoe fits. Although some European manufacturers are now making shoes that come in wide and extra-wide widths, typically customers must try on several pairs to find a good fit. A more current version of the Continental European system lengthens templates by 1.5 centimeters.
American shoe sizes are designated both by length (measured in inches, expressed as numerals) and width, measured in inches around the widest part of the foot (expressed as letters – AA, B, C, D, EEE). Unless they have hard-to-fit feet, most consumers can rely on the sizes marked on shoes and packaging to find a proper fit.