While different parts of the world have different standards for shoe sizes, it is possible to convert from one to another. Just as most countries measure small lengths in either inches or millimeters, most systems for shoe sizes are also either based on inches or millimeters (in Korea, shoe sizes are actually given in millimeters). Thus, just as it is possible to convert from units of inches to units of millimeters, it is also possible to convert from any shoe sizing system to any other shoe sizing system, or even actual inches or millimeters.
Find the shoe size in U.S. mens' size. For U.S. womens' sizes, this can be done by simply subtracting 1 1/2 from the womens' size. For U.K. mens' sizes, add 1/2, and for U.K. womens' sizes, add 1. For sizes from other countries, there are charts available to assist with the conversion.
Take the U.S. men's shoe size, multiply it by 1/4 and then add 8 1/8 to get the shoe size in inches. For example, if the U.S. men's shoe size is 1.5, the converted shoe size would be 8 1/2 inches.
Multiply the result from Step 2 by 25.4, which will convert the result from inches to millimeters. Continuing the example from Step 2, 8 1/2 inches x 25.4 = 215.9 millimeters.