Convert shoe sizes between US men's and women's, UK, EU, India, Japan and Mondopoint via foot length, using the ISO/TS 19407 formulas.
US men's 10 fits a foot about 270.9 mm long; the nearest EU (Paris points) size that isn't smaller is 43.
Formulas from ISO/TS 19407 (adult sizes); each already includes the standard allowance between foot and last.
ISO/TS 19407 rounds converted sizes up to the next size (here in steps of 0.5), for comfort.
Adult shoe sizes in the US men's, US women's, UK, Indian, EU, Japanese and Mondopoint systems all map to a foot length. The converter turns a size into a foot length L in millimetres with the ISO/TS 19407 formulas, then reads it on the target scale: EU = 3L/20 + 2 and UK = 3L/25.4 − 23, with US men's one size above UK and US women's two above.
Use it when buying shoes labelled in another country's system. The default, US men's 10, corresponds to a 270.9 mm foot, which is EU 42.6 before rounding and EU 43 after. Converted sizes round up to the next half size (5 mm steps for Japan and Mondopoint), as the specification recommends, so the answer errs towards room rather than a tight fit.
Brands cut their lasts differently, so compare the result with the brand's own foot-length chart. The formulas cover adult feet from 200 to 340 mm; children's sizes follow different formulas.
Checked against: Wikipedia ISO/TS 19407 adult table: US men 10 = UK 9 = US women 11 at 270.9 mm; the next sizes at or above that length are EUR 43 (273.3 mm) and Mondopoint 275
Checked against: Wikipedia ISO/TS 19407 table: EUR 42 = 266.7 mm, where UK 8.5 / US men 9.5 sit; FIA women's scale = men's + 1
Checked against: Wikipedia ISO/TS 19407 table: 250.0 mm row lists Mondopoint 250 and EUR 39.5; UK 6.5 is 249.8 mm, so the next UK size up is 7 (254.0 mm)
Checked against: Wikipedia ISO/TS 19407 table: UK 12 = 296.3 mm; EUR 46.5 = 296.7 mm is the next size up
EU 43. Under ISO/TS 19407, US men's 10 fits a 270.9 mm foot, which works out to EU 42.6; converted sizes are rounded up to the next half size, giving 43. The same foot is UK 9, India 9, US women's 11, Japan 27.5 cm and Mondopoint 275.
Subtract 1 on the FIA (Footwear Industries of America) scale used here: US women's 9 is US men's 8. Many US brands use the common scale instead, where women's sizes are men's plus 1.5, so women's 9 is men's 7.5. UK sizing is nominally the same for men and women, although some manufacturers number women's UK sizes differently.
They count in different units. One EU size is a Paris point, 2/3 cm (6.67 mm) of shoe length; one UK or US size is a barleycorn, 1/3 inch (8.47 mm). A full UK size therefore spans 1.27 EU sizes, and no adult UK size falls exactly on a whole or half EU size, so every conversion between the two rounds.
Mondopoint (ISO 9407) sizes a shoe by the foot length it fits, in millimetres, so a 270 mm foot is Mondopoint 270. It is the main system in Japan, which writes it in centimetres (27 cm), and in China, Russia and South Korea. Ski boots, skates, pointe shoes and NATO military footwear also use it.
Yes. Adult shoes in India, like those in the UK, Ireland, Pakistan and South Africa, are sized in barleycorns from the length of the last, so India 9 is UK 9 and US men's 10. Mondopoint is an optional second system in India, as it is in the UK.
Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 5 worked examples whose answers come from independent sources; for example, “US men's 10 in EU” is checked against Wikipedia ISO/TS 19407 adult table: US men 10 = UK 9 = US women 11 at 270.9 mm; the next sizes at or above that length are EUR 43 (273.3 mm) and Mondopoint 275.
ISO/TS 19407:2015 — Footwear — Sizing — Conversion of sizing systems; Wikipedia — Shoe size: ISO 19407 formulas and adult size equivalence table.
5 worked examples with independently sourced answers ship with this calculator. They run in the test suite; you can run them here too.
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