US Women’s Size 9 to UK

Every shoe-size system is really a coded way of describing one thing — the length of your foot — but each country codes it differently, and women’s scales sit differently again from men’s. In the UK and US the sizes come from the old English “barleycorn” of one-third of an inch per step, and for women a US size runs exactly two numbers above the UK size, so a UK 6 is a US 8. (A women’s US size is also about one and a half sizes above the men’s size for the same foot.) Continental Europe uses the Paris point instead — two-thirds of a centimetre per size — and the EU number is unisex, based purely on the last length, so the same EU number can be a men’s or a women’s shoe. Because these systems each have their own step size and starting point, converting between them is a straight-line formula with a slope and an offset, not a single ratio; this tool solves that formula in both directions. The simplest systems just state the foot length outright: Mondopoint (the international standard) and the Korean and Chinese systems use millimetres, while Japan uses centimetres, so a 240 mm foot is Mondopoint 240, Japan 24 and, in round numbers, a US women’s 8 / UK 6 / EU 39. Real shoes vary by brand and last shape, so treat the result as a starting point and round to the nearest half size — and if you can, measure your foot in millimetres, which every one of these systems is ultimately built on.