The Same 38 Is Ten Millimetres Apart

Where a 1 is bigger than a 13

The children's US scale counts up to 13 and then starts again at 1 — the switch to what shops call Youth. On the table, 175 mm is a US 13 and the very next row, 180 mm, is a US 1. Nothing shrank; the numbering restarted. This is the single most common way a pair bought online for a child comes back, because a parent reading "US 1" after a "US 13" reasonably concludes the shoe is smaller. The converter marks the row where the restart happens instead of leaving it to be discovered on delivery, and the millimetre column runs straight through it without a break.

Measuring the foot takes a minute and settles it

Stand with your heel against a wall, mark the tip of the longest toe — which is not always the big one — and measure from the wall to the mark. Do it at the end of the day, when the foot is at its largest, and do both, because they differ and the larger one is the one that has to fit. That number is the row to read, and it is also the number worth keeping: a brand's own chart is written in millimetres too, so a foot of 245 mm can be checked against the maker's table rather than against a general conversion. The equivalences here are a convention, not a standard, and two pairs both marked 38 can differ by a full size — the foot length is the only figure that does not move from maker to maker.

Frequently asked questions

Should running shoes be bought a size up?

The usual advice is a finger's width — roughly 5 to 10 mm — of space in front of the longest toe, because the foot lengthens under load and swells over a long run. Expressed in millimetres that is a clear instruction: measure 245, look for a shoe built around 250 to 255. Expressed as "a size up" it is not, since a size is worth 5 mm in one column of this table and a full 10 in another.

Why do UK and US numbers differ by about one?

Both count in barleycorns — a third of an inch per size, which is where the odd half-steps come from — but they start counting from different zero points, so the American number runs about one ahead of the British one for men and around two ahead for women. Neither is wrong; they are two rulers with the same spacing and different origins, which is exactly why the conversion cannot be done in your head.

Is there an actual standard?

Yes, and it is the millimetre column. Mondopoint labels a shoe by the length of the foot it is meant for, in millimetres, optionally with the width — which is why it is what armies and safety footwear use, and why the Japanese retail scale, being the same idea in centimetres, is the one consumer scale that means something on its own. It has never displaced the national numbers in shops, so the practical version of the standard is: find your millimetres once, and treat every other number as a translation.