Shoe Size Converter
Shoe sizes have a real arithmetic behind them, so this converts from the definitions and shows the working — rather than looking up a table whose origin nobody can name.
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Where the numbers come from
A Paris point — the unit of EU sizing — is exactly two-thirds of a centimetre. A barleycorn — the unit of UK sizing — is exactly one third of an inch. Those are definitions, not conventions, which is why this page can print the arithmetic instead of asking you to trust it.
What is not a definition is the allowance between the last and the foot inside it, and the offsets between US men's, US women's and UK. Those are trade convention, and brands deviate from them. That is exactly why every result here sits next to the foot length it came from: the centimetres are solid, the size number is an inference.
Why apparel sizes are not on this page
Because there is nothing to convert. S/M/L and the national numeric apparel scales have no derivable relationship — only each brand's own block. The universal conversion charts circulating online are one or two brands' tables presented as a general truth, and following them produces returns that the seller pays for.
The thing that does work is publishing the garment's actual measurements — chest, waist, length — beside whatever size label you use. A buyer can check those against something they already own, which is more than any conversion chart offers.
Every check this tool runs (7 rules)
SHO-M01 Measure the foot, not the old shoe
Foot length in centimetres is the only quantity that does not change between brands. Every size number here is derived from it and shown with its working, so you can see how far a conversion is really carrying you.
Fix: Stand on paper, mark heel and longest toe, measure the distance.
Source: The arithmetic is from the definitions of the units themselves: a Paris point is exactly 2/3 cm and a barleycorn is exactly 1/3 inch. The last-to-foot allowance and the US-to-UK offsets are industry convention rather than definitions, and brands deviate from all of it — which is why every result here is presented alongside the foot length that produced it.
SHO-B01 Brands deviate, and the deviation is larger than the conversion
The unit arithmetic is exact, but the step from foot length to a marked size depends on the last, and lasts differ by brand and often by model within a brand. A conversion is a starting point for a size chart, never a substitute for the brand’s own.
Source: The arithmetic is from the definitions of the units themselves: a Paris point is exactly 2/3 cm and a barleycorn is exactly 1/3 inch. The last-to-foot allowance and the US-to-UK offsets are industry convention rather than definitions, and brands deviate from all of it — which is why every result here is presented alongside the foot length that produced it.
SHO-H01 Half sizes do not exist everywhere
EU sizing is a whole-number scale of Paris points, so an EU half size is a brand’s own invention rather than part of the system. Converting a UK half size into EU therefore lands between two real sizes.
Source: The arithmetic is from the definitions of the units themselves: a Paris point is exactly 2/3 cm and a barleycorn is exactly 1/3 inch. The last-to-foot allowance and the US-to-UK offsets are industry convention rather than definitions, and brands deviate from all of it — which is why every result here is presented alongside the foot length that produced it.
SHO-W01 Men’s and women’s US sizes are different scales
A US women’s 8 and a US men’s 8 are not the same shoe. The offset from UK sizing differs between them, which is why converting without knowing which scale you are in produces an error of a size and a half.
Source: The arithmetic is from the definitions of the units themselves: a Paris point is exactly 2/3 cm and a barleycorn is exactly 1/3 inch. The last-to-foot allowance and the US-to-UK offsets are industry convention rather than definitions, and brands deviate from all of it — which is why every result here is presented alongside the foot length that produced it.
SHO-A01 Apparel sizes cannot be converted, and this tool will not pretend
There is no arithmetic relationship between S/M/L and any national numeric apparel scale — only each brand’s own block. The universal conversion charts circulating online are one or two brands’ tables presented as a general truth. Publishing one would state something uncertain in a confident voice, and the returns land on the seller.
Fix: Publish the garment’s actual measurements — chest, waist, length — alongside whatever size label you use. That is the only thing a buyer can check against something they own.
Source: Own engineering position, deliberately not a data table: no standards body publishes a cross-brand apparel size mapping, and EN 13402, which defines how to label body measurements, is a paid standard this project does not hold.
SHO-R01 Size outside the range this arithmetic covers
The conversion is linear and only meaningful across the ordinary adult range. Outside it — children’s scales in particular — the systems stop lining up and separate conventions take over.
Source: The arithmetic is from the definitions of the units themselves: a Paris point is exactly 2/3 cm and a barleycorn is exactly 1/3 inch. The last-to-foot allowance and the US-to-UK offsets are industry convention rather than definitions, and brands deviate from all of it — which is why every result here is presented alongside the foot length that produced it.
SHO-V01 Converted, with the working shown
Each size is derived from the foot length, and the arithmetic is printed next to it.
Source: The arithmetic is from the definitions of the units themselves: a Paris point is exactly 2/3 cm and a barleycorn is exactly 1/3 inch. The last-to-foot allowance and the US-to-UK offsets are industry convention rather than definitions, and brands deviate from all of it — which is why every result here is presented alongside the foot length that produced it.
Every rule here is this project’s own engineering, derived from the unit definitions. No standards body publishes a cross-brand size mapping, and this page does not invent one.