How shoe size systems line up
There is no single world standard for shoe size, only four common scales that all approximate the same thing: the length of your foot. The US and UK scales count in barleycorns, an old unit of one third of an inch, so each half size adds about one sixth of an inch. US men and UK numbers differ by a constant 1, so a US men 9 is a UK 8. US women are offset from US men by 1.5, so a US women 8.5 and a US men 7 are the same shoe. The EU scale, called Paris points, counts in two-thirds-of-a-centimeter steps, which is why EU sizes climb faster than US ones. Japan, and increasingly Chinese and Korean brands, simply print the foot length in centimeters, the system known as Mondopoint, which is by far the clearest of the four.
The table above is built on the usual anchor points: EU 36 equals US women 6, UK 3.5 and 23 cm; EU 40 equals US men 7, UK 6 and 25 cm; EU 44 equals US men 10, UK 9 and 28 cm. Pick the number you already know, choose which system it belongs to, and every other column is filled in.
How to measure your feet
Measure late in the day, when feet are at their largest, and wear the socks you plan to use. Tape a sheet of paper to a hard floor against a wall, stand on it with your heel touching the wall, and put your weight on that foot. Have someone mark the paper at the tip of your longest toe, which is not always the big toe. Measure from the wall to the mark in centimeters, then repeat for the other foot: most people have one foot a few millimeters longer, and you should buy for the larger one.
Add roughly 1 cm of toe room to the measured length before reading the chart, or up to 1.5 cm for running shoes, since feet swell and slide forward on downhills. A 25 cm foot therefore usually buys a 26 cm shoe, which is a US men 8. Width matters too: US brands label D as standard for men and B for women, with 2E and 4E for wide. If your foot measures wide, size up half a size only as a last resort, because a longer shoe also moves the arch support to the wrong place.
Brand variation and online shopping
Treat any conversion as a starting point, not a guarantee. Two shoes labeled US 9 from different brands can differ by a third of a size, and running shoes, dress shoes and boots from the same brand often run differently. Italian dress shoes tend to run narrow and long, so many buyers drop half a size; skate and basketball shoes are often roomy. Some brands publish an official length in centimeters for each size on the product page, and that number beats any chart.
Kids add another layer, because US youth sizes restart at 1 after 13 in little kids, and a big kids 7Y is generally the same last as a US men 7 at 25 cm. Children outgrow shoes every four to six months, so measure often and allow about 1.5 cm of growing room. When ordering from overseas, check the return policy first, and prefer retailers that list the centimeter length alongside their local size.