There are many different measurements of shoe sizes, and while there are standards to shoe sizes for shoe makers, the size of a shoe can vary by manufacturer regardless of the size quoted on the shoe's label. Shoe sizes can also vary by gender, as well as by age and by the shoe's country of origin. According to Warwick Cairn's "About the Size of It," the insole size of shoe-sizes in American and British shoes increases by thirds-of-an-inch, or barleycorns, while Paris Points are the most common measurement outside of the English speaking world, specifically in Europe.
Find the size of the shoe you are attempting to convert to inches.
Identify which country the shoe is from, and thus whether the shoe size is on the American, Japanese, French, English, Mexican, Danish, New Zealand, Italian, German, Australian, Spain, Greek, or Brazilian scale.
Determine the intended gender of the shoe.
Refer to the "International Shoe Size Conversion Chart" and locate the shoe's size by country and gender.
Follow the chart from the shoe size to the top row of the same column and identify the equivalent in inches.
Although there are standards for shoe sizing in place, shoe sizes can vary slightly. Because American and English size intervals are marked by 1/3 of an inch, and because half sizes are made for many of these shoe sizes, according to the Bata Comparative Size Chart, a shoe a half-size up or down from your usual size may fit as well.