Shoe sizes are a mess for a simple historical reason: every country numbered feet differently, nobody ever agreed to reconcile the systems, and brands quietly bend even their own country's scale when it suits the shoe. So a US men's 9 is a UK 8.5 is an EU 42, except when it is an EU 43 because that particular factory says so. This converter gives you the standard conventions all in one place, and it is honest about where they wobble.
One thing to hold onto before you order anything: these charts are conventions, not law. Brands vary by up to half a size, and EU sizing varies the most. Use the result here to narrow the search, then check the brand's own chart if the purchase is hard to return.
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How to measure your foot
Skip the guessing and get a real number. Stand on a sheet of paper with your heel touching a wall, weight on the foot. Mark the tip of your longest toe (which is not always the big toe). Measure from the edge of the paper at the wall to the mark, in inches or centimeters. Do both feet, because almost everyone has one foot slightly longer, and size to the longer one. Evening is the best time to measure since feet swell a little over the day, and that is the foot your shoes actually have to fit.
The formulas
US men's is the anchor system here: every other size is a fixed offset from it. The foot length formulas are the standard Brannock device scale, where each full size is a third of an inch of foot. Centimeter inputs convert at 1 inch = 2.54 cm, and every displayed size is rounded to the nearest half size because that is the smallest increment shoes come in.
Worked example
Full conversion chart
Every row is computed with the formulas above: UK is a half size below US men's, EU is US men's plus 33, and women's is US men's plus 1.5.
| US men's | UK | EU | US women's |
|---|---|---|---|
| 6 | 5.5 | 39 | 7.5 |
| 6.5 | 6 | 39.5 | 8 |
| 7 | 6.5 | 40 | 8.5 |
| 7.5 | 7 | 40.5 | 9 |
| 8 | 7.5 | 41 | 9.5 |
| 8.5 | 8 | 41.5 | 10 |
| 9 | 8.5 | 42 | 10.5 |
| 9.5 | 9 | 42.5 | 11 |
| 10 | 9.5 | 43 | 11.5 |
| 10.5 | 10 | 43.5 | 12 |
| 11 | 10.5 | 44 | 12.5 |
| 11.5 | 11 | 44.5 | 13 |
| 12 | 11.5 | 45 | 13.5 |
| 12.5 | 12 | 45.5 | 14 |
| 13 | 12.5 | 46 | 14.5 |
| 13.5 | 13 | 46.5 | 15 |
| 14 | 13.5 | 47 | 15.5 |
| 14.5 | 14 | 47.5 | 16 |
| 15 | 14.5 | 48 | 16.5 |
Why the charts disagree
Three systems, three separate origin stories. US and UK sizes both come from the English barleycorn (a third of an inch per size), but the two countries picked different starting points, which is where the half-size gap comes from. EU sizes use the Paris point, two thirds of a centimeter per size, measured on the inside length of the shoe rather than the foot. Since the shoe's internal length depends on how much toe room the maker builds in, EU numbers drift the most: some brands' charts sit a full size away from the US 9 = EU 42 convention this page uses. The women's offset has its own quiet disagreement, with most athletic brands using 1.5 sizes and a few traditional makers using 2. None of this is anyone lying to you. It is just a hundred years of nobody being in charge. Expect any conversion to be right within half a size, verify against the brand's own chart for anything expensive, and when in doubt, trust your measured foot length over any label.
Sizing a kid instead? See the kids shoe size conversion. Converse famously runs a half size large; the Converse size chart handles that. And if you are on a measuring spree, the ring size calculator works the same honest way.