Shoe Size Converter
Convert shoe sizes between US, UK, EU and centimetres for men, women and children, with a warning that brand sizing varies enough to make charts approximate.
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| US | UK | EU | Foot (cm) |
|---|
Why no shoe size formula exists
US and UK sizes step by a barleycorn — one third of an inch, 8.4667 mm — so a half size is 4.2333 mm. European sizes step by a Paris point, two thirds of a centimetre, 6.6667 mm.
The ratio between a US half size and an EU size is exactly 127/200. Walk up both ladders and the rungs never line up again — not at any size anyone wears. So every published chart is a rounding of a mapping that cannot be exact, and different manufacturers round differently. The note above about brands varying is the honest part of the table.
A US number means two different feet
This one is worth measuring rather than assuming, and the answer came out the opposite way round from what I expected. Take every size value that appears in both charts here and compare the foot length each one states for it:
| System | Shared values | Agree exactly | Mean disagreement | Worst |
|---|---|---|---|---|
| US | 11 | 0 | 12.7 mm | 17 mm |
| UK | 8 | 2 | 1.1 mm | 2 mm |
| EU | 7 | 2 | 1.7 mm | 6 mm |
The US column is the inconsistent one, by a wide margin, and not one of its 11 shared values agrees. A men's US 9 and a women's US 9 are about 13 mm apart — 1.9 EU sizes, nearly two whole sizes hiding behind the same number.
UK numbers mean very nearly the same foot either way. That is the reverse of the usual complaint that UK sizing is the confusing one, and it explains the offsets: US sits 0.5 above UK for men and 2 above UK for women. Both offsets are perfectly constant within their own chart — the gender convention lives entirely in the gap between them.
And the chart is not internally straight either
If the foot-length column were generated from the size it would be a straight line: one US size is always one barleycorn, 0.8467 cm. Fitting a line through the published numbers and measuring how far they stray:
| Chart | Fitted slope | Theory | Worst deviation |
|---|---|---|---|
| men | 0.8951 cm | 0.8467 | 3.0 mm |
| women | 0.8516 cm | 0.8467 | 1.0 mm |
The women's column sits close to the theoretical step. The men's climbs faster than a barleycorn and wanders by up to three millimetres. Neither is wrong — they are compiled conventions, not formulas — but it does mean the columns cannot all be right at once.
Which gives the one practical instruction worth taking away: measure your foot in centimetres and use that column. It is the only one that refers to a physical object rather than to a numbering convention, and it is the only one a manufacturer cannot quietly redefine.
One note on how this converter behaves: it snaps whatever you type to the nearest row and says "(closest match)" when it is not exact. Over foot lengths from 22 to 31 cm in millimetre steps, only 16% land on a row. The worst gap to any row is 4.0 mm, about 0.6 of an EU size — so the label is doing real work rather than being modest.
How to use
- Measure your foot length in centimetres.
- Pick the system and category you are converting from.
- Read the equivalent sizes across systems.
- Treat every result as a starting point, not a guarantee.
Frequently asked questions
How accurate is any shoe size chart?
Approximate at best. Sizing is not standardised between manufacturers, and half a size of variation between brands is entirely normal — a full size is not unusual. Foot length in centimetres is the only figure that means the same thing everywhere, which is why it is the most useful number to know.
What is the difference between US and UK sizes?
UK sizes run about one size smaller than US men's sizes — a UK 9 is roughly a US 10. Women's sizing adds another offset, and different brands apply it differently, which is why converting women's sizes across systems is less reliable than converting men's.
How does EU sizing work?
In Paris points, each two-thirds of a centimetre. The system measures the last rather than the foot, so it includes an allowance that varies by manufacturer. EU sizes have no half sizes in principle, though many brands add them anyway.
When should I measure my feet?
In the evening, standing, wearing the socks you intend to use. Feet swell through the day by up to half a size, and they spread under body weight — measuring seated in the morning reliably produces a size that pinches by the afternoon.
Are my feet the same size as each other?
Probably not. A difference of up to half a size between feet is common and normal. Fit the larger foot and adjust the other with lacing or an insole, since a shoe that is too short cannot be corrected.
Do feet change size in adulthood?
Yes, gradually. Ligaments loosen and arches flatten over decades, so feet tend to lengthen and widen with age. Pregnancy can produce a permanent change. Anyone who has worn the same nominal size for twenty years is worth remeasuring.
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