Shoe Size Converter

This calculator works in two separate passes, and Gender is read at both of them independently. First, it converts whatever you typed in the Source System you chose into a common foot length in centimeters: US and UK follow a men/women/kids-specific linear formula (men and women subtract from Size before scaling by 0.847 cm per half-size, line 20; kids instead adds 0.5 to Size at that stage, the one sign flip in the whole input branch, compare line 24 to line 33), EU uses one gender-neutral formula that never reads Gender at all (line 16), and CM simply passes your number straight through as the foot length, also without reading Gender (lines 11-13). Second, once it has a foot length in centimeters, it converts that back out to every system, and this second pass reads Gender again -- so if you entered your size in CM, Gender never touched step one but still fully determines the US and UK sizes you get back in step two. The output-side US and UK formulas mostly mirror the input-side ones, with one more asymmetry: Kids' UK conversion subtracts half a step at this stage (line 50) after having added it going in (line 33) -- the only system/gender combination where the input and output formulas use opposite signs.

EU size, in both directions, never depends on Gender. Mondopoint reports the same foot length as Foot Length (cm), just expressed in millimeters -- ten times the centimeter figure, rounded to a whole number (line 61) -- rather than being an independently derived size. US, UK, and EU outputs are each floored at a minimum plausible size (1, 0.5, and 15 respectively) so an unusually small input cannot report a negative or nonsensical size, though those floors sit far below any size reachable from the calculator's supported input range (lines 56-58).