EU, US, UK Shoe Sizes: Why Every Conversion Chart Disagrees

Every online shoe conversion chart quietly disagrees with the others, and the reason is not sloppiness. The world’s major shoe size systems were invented separately, count in different units, and were never designed to convert into each other. Understanding where the numbers come from explains why the charts fail and what to do instead.

Paris points and barleycorns

European sizes count the length of the last — the mold the shoe is built on — in Paris points of two-thirds of a centimeter, roughly 6.67mm per size. The system traces back to nineteenth-century French practice and spread because it applied to men’s and women’s shoes alike. British and American sizes count in barleycorns, a third of an inch, about 8.46mm per size, with different zero points. Crucially, no EU size is set by law: there is no enforcement body defining what EU 42 must measure, and ISO’s technical specification for converting between systems is a recommended compromise, not a mandate. The units alone guarantee that no single offset translates one system into the other across the whole range.

The US gender offset most people get wrong

US sizing runs separate scales for men and women built on different zero points, so the same foot takes two different American numbers depending on which shelf the shoe came from. US men’s sizes sit roughly one barleycorn above UK sizes; US women’s sizes run about two above UK, with the exact gap varying between one and a half and two depending on the brand. This is the single most common conversion error: applying a men’s offset to a women’s purchase, or assuming the women’s-to-EU gap matches the men’s. EU sizing, by contrast, uses one scale for both, which is why the same person can be a 42 in Europe and two different US numbers in two different stores.

The last matters more than the number

Even within one system, the same size fits differently across brands because the last differs — each maker chooses its own toe shape, instep height, and the allowance added beyond the foot, which can reach a couple of centimeters. Analyses of hundreds of production lasts have found the internal width at the ball varying by more than a centimeter between brands at the same labeled size. That is wider than the gap between most adjacent width letters, which makes last shape a bigger fit factor than any number on the box. The same logic runs through our loafer fit guide: fit lives in the last, not the label.

What to measure instead

Skip the size-to-size conversion entirely. Measure both feet standing, late in the day, heel against a wall, and note the longer foot in centimeters. Then read that length against the specific brand’s own size chart, which reflects its actual lasts rather than a generic table. A Brannock device does the same job for length and width together, but a wall and a piece of paper are nearly as accurate. And treat reviews as fit data — comments about a model running narrow or long describe the last, which is the information conversion charts cannot carry. That habit, checking what the maker actually specifies before trusting the label, is the same one behind our spec-sheet-first sneaker guide.