Why every conversion routes through centimeters
US, UK, and EU sizing all describe the same underlying thing — foot length — but each system was built around a different scale and starting point, so there's no clean multiply-by-X shortcut directly between them. This tool sidesteps that by converting whatever you enter into centimeters (the Mondopoint measurement, essentially foot length itself) first, then converting from centimeters into the target system. That intermediate step is exactly what the step-by-step breakdown shows.
US and UK: an offset, then a scale factor
US and UK sizes both convert to centimeters the same way — add a fixed offset to the size, then multiply by a constant — but the offset differs by both country and gender, which is why the two systems don't line up with a simple subtraction.
CM = (US size + 22) × 0.847 (men)
CM = (US size + 20.5) × 0.847 (women)
CM = (UK size + 23) × 0.847 (men)
Working a men's US 9 through: (9 + 22) × 0.847 = 26.3 cm. That 26.3 cm figure is the real, brand-independent number — the US, UK, and EU labels attached to it are just different ways of naming the same foot length.
EU sizing and the Paris point
European sizing comes from an older French system where each size step, a "Paris point," equals two-thirds of a centimeter. Scaled out, that gives a simple relationship between EU size and foot length in centimeters.
EU size = (CM × 1.5) + 2
26.3 cm → (26.3 × 1.5) + 2 = 41.5 → EU 41
That's why a men's US 9 and a UK 8 both land close to an EU 41-42: they're all naming roughly the same 26 cm foot, just counted in different-sized steps from different starting points.
Why men's and women's sizes don't share a scale
For the same foot length, US women's sizing runs about 1.5 to 2 sizes larger in number than men's — a men's US 9 and a women's US 10.5 to 11 both correspond to roughly the same physical foot. That's a labeling convention, not a difference in how feet are measured, which is why gender matters as an input here: converting a women's size as if it were a men's size (or the reverse) throws the result off by that same 1.5-2 size gap.
What conversion can't tell you
A converted size gets you to the right neighborhood, not necessarily the exact fit. Brands cut shoes on different lasts — the foot-shaped mold a shoe is built around — so a running shoe, a dress shoe, and a boot in "the same" converted size can fit noticeably differently in width and volume even when the length matches. When it's available, a brand's own size chart (often based on directly measured foot length in cm) is more reliable than a generic conversion for that specific pair.
Other sizing and measurement conversions
For other clothing and body-measurement conversions, the bra size calculator works through band and cup sizing across US, UK, and EU systems the same way, and the height calculator covers metric-imperial height conversions.