ReckonBoxOne foot, five numbers
A shoe size converter maps a size in one country's system to the others, and to the foot length underneath them all. A US men 9 comes out as a UK 8.5, an EU 42, and a foot about 26 centimetres long.
The reason the numbers look unrelated is that each system starts counting from a different place. US and UK sizing measures the shoe in barleycorns, an old unit of a third of an inch, while Europe measures in Paris points of two thirds of a centimetre. Same foot, three rulers. This tool converts between all of them and, more usefully, shows the foot length they all trace back to.
The scales, and how they line up
US and UK sizes share the barleycorn system, so a UK size sits about half a size below the US men size. A US men 10 is a UK 9.5, a US men 9 a UK 8.5.
EU sizing is the outlier. It runs on the Paris point and is unisex, so it climbs on a different, larger scale: that US men 9 lands near an EU 42. The step between EU sizes is smaller than a full US size, which is why EU numbers rise faster. Japan keeps things refreshingly plain by sizing shoes in centimetres of foot length, so a Japan 26 is simply a 26 centimetre foot, and China tracks close to the EU scale for adults.
Men to women, and the offset nobody agrees on
Converting a men size to a women size is where charts start disagreeing. For the same foot length, you add about 1.5 to a US men size to reach the US women size, so a men 8 is roughly a women 9.5. Look across sources and the gap is quoted anywhere from 1 to 2 sizes, because men and women shoes are built on different lasts and the number is doing double duty as a fit adjustment. The honest answer is to compare foot length, which does not care about anyone's marketing.
Foot length is the input that travels
A 26 centimetre foot is a 26 centimetre foot in Milan, Manchester, or Osaka. Size numbers drift by half a size between brands; foot length does not move at all. To measure, stand on a sheet of paper with your heel to a wall, mark the tip of your longest toe, and measure the distance in centimetres. Feet also swell through the day, so measure in the afternoon and use the larger foot. This tool converts from that length as happily as from any size number.
Why a conversion is a start, not a promise
A size describes the last, the mould a shoe is built around, and lasts vary by brand, by style, and by model within a brand. Two shoes both stamped US 9 can fit half a size apart, and width, which these length-only charts ignore entirely, changes the fit again. Use the conversion to get in the right range, then check the brand's own size guide and try the shoe where you can.
The single most reliable thing you can carry between size systems is not a number at all, it is the length of your own foot in centimetres.
Frequently asked questions
How do US, UK, and EU shoe sizes relate? US and UK sizes both use the barleycorn system, a third of an inch per size, so a UK size is about half a size below the US men size: a US men 9 is a UK 8.5. EU sizes use the Paris point, two thirds of a centimetre per size, and run on a different, larger scale, so that same shoe is roughly an EU 42. Every scale has a different starting point, which is why the numbers look unrelated.
How do I convert a men size to a women size? For the same foot length, add about 1.5 to a US men size to get the US women size, so a men 8 is roughly a women 9.5. Sources put the gap anywhere from 1 to 2 sizes, because men and women shoes are built on different lasts, so the number is a guide rather than a rule. The reliable move is to compare foot length in centimetres, which this tool shows for every size.
Why is measuring my foot length more reliable? Foot length is the one input that does not change between brands or countries, while size numbers drift by half a size or more depending on the maker. A 26 centimetre foot is a 26 centimetre foot everywhere. Stand on a piece of paper, mark heel to longest toe, measure in centimetres, and match that to the chart. This tool converts from a foot length as readily as from a size.
Do Japan and China use their own shoe sizes? Japan sizes a shoe by foot length in centimetres, so a Japan 26 is a 26 centimetre foot, which lines up with the foot length this tool reports. China sizes vary but track close to the EU scale for adults, so an EU number is a good stand-in. Because all of these ultimately point back to foot length, converting through centimetres is the safest path between any two systems.
Why do sizes still feel off between brands? Because a size number describes the last, the mould a shoe is built around, and lasts differ by brand, style, and even model. Two shoes marked US 9 can fit half a size apart, and width adds another variable these length-only charts ignore. Treat any conversion as a starting point, then check the brand size guide and, where you can, try the shoe on.