How this calculator works
Shoe sizes are all derived from foot length, but each system counts differently. The Brannock approach used here converts the foot length in inches to a US men's size by multiplying by three and subtracting 22, because each US size is one third of an inch. Women's US sizes run about one and a half sizes higher than men's, and UK adult sizes run one size below US men's. European sizes are based on the length of the last in centimetres, approximated here as 1.5 times the foot length plus 2.25. Japanese and Mexican sizes are close to the foot length in centimetres, and Korean sizes are the foot length in millimetres, rounded to the nearest five. These are approximations: makers use different lasts, so treat the result as a starting point.
Formula
foot length in inches = foot length in cm / 2.54. US men = 3 x foot inches - 22. US women = US men + 1.5. UK adult = US men - 1. EU = 1.5 x foot cm + 2.25. JP / MX = foot cm. Korea = foot cm x 10, rounded to 5. For children, US child = 3 x foot inches - 9.67.
Worked example
A foot 27 cm long is 10.63 inches. Three times that minus 22 is 9.89, so US men 10. US women is about 11.5, UK 9, EU 42.75 rounded to 43, Japanese 27 and Korean 270 mm.
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Frequently asked questions
Should I measure both feet?
Yes. Most people have one foot slightly longer. Measure both, preferably in the evening when feet are largest, and use the longer measurement. Always try on the actual shoe, because the last shape matters as much as the length.
Why do the formulas give half sizes?
The systems are built in half-size or smaller increments, so a foot length often falls between two whole sizes. The calculator rounds to the nearest half size. If you are between sizes, choose the larger size for sports shoes and the smaller for dress shoes that will stretch.
Are these conversions exact?
No. They follow the common formulas, but brands use different lasts, widths and size charts, and a US 9 in one brand can fit like a US 10 in another. Use the conversion to narrow the range, then rely on the maker's chart or a fitting.
What about width?
These formulas cover length only. Shoe width is a separate scale, usually lettered from narrow to wide, and a wide foot may need a larger size in a narrow last. The foot length and the maker width chart together give a better fit.