Shoe size converter
Stand on a sheet of paper with your heel against a wall, mark the end of the longest toe, and measure. Do it late in the day with the socks you will wear, and measure both feet — most people have one that is a few millimetres longer, and the shoe has to fit that one. Adding five to ten millimetres of toe room on top is normal for walking shoes and essential for running.
Shoe sizing is not standardised between brands and differs markedly between sports and dress styles. Foot length in centimetres is the only reliable common reference.
Shoe sizing systems are unrelated scales over the same foot length. A 26 cm foot is roughly EU 41, UK 7.5 and US men 8.5. Japanese sizing is simply the foot length in centimetres, which makes it the most transparent of the four.
How to convert shoe sizes
The scales differ because they measure different things. The Paris point used in EU sizing is two thirds of a centimetre per size, applied to the last rather than the foot. UK sizes use barleycorns — a third of an inch — and start from a different zero. US sizes are the UK scale shifted, and differently for men and women, which is why a straight conversion between US men and US women is a fixed 1.5 rather than anything principled. Only foot length in centimetres is common to all of them.
Questions
About EU 42, and US men 9. The exact conversion varies slightly between brands.