A US women’s 7 is a UK 5, and on the scale this site uses it is about an EU 37.5 and a Japanese 23.5. The four labels describe the same foot, about 237 mm long, but each one counts in a different unit and starts from a different zero. Once you know the units, most of the confusion on brand size charts becomes predictable.
Three units, three starting points
UK and US sizes count barleycorns. A barleycorn is an old English length of one third of an inch, about 8.47 mm. One whole UK or US size is one barleycorn, and a half size is half of that, about 4.2 mm. The Wikipedia summary of the system gives the adult UK formula as 3 × last length in inches − 25, where the last is the foot-shaped form a shoe is built on. Because the last is longer than the foot, the same article gives the foot-based version as roughly 3 × foot length in inches − 23, which adds two barleycorns of room.
EU sizes count Paris points. A Paris point is two thirds of a centimetre, about 6.67 mm, and the European number is the length of the last in Paris points, counted from zero: 1.5 × last length in centimetres. From the foot, the approximation becomes 1.5 × foot length in cm + 2, again adding two size steps of allowance.
Mondopoint and Japanese sizes count millimetres of foot. Mondopoint labels the foot, not the last, by length (and in full form, width). Japan uses this approach under the national standard JIS S 5037, with the foot length printed in centimetres in 5 mm steps. A Japanese 23.5 means a foot about 235 mm long.
So the step sizes do not match. One UK or US size is about 8.47 mm, one EU size about 6.67 mm, and one Japanese step 5 mm. A single UK size covers roughly 1.27 EU sizes. That mismatch is why a chart cannot map whole and half US sizes onto EU sizes without rounding somewhere.
The two US women’s scales
US women’s sizes are built on US men’s sizes, and there are two common offsets. Wikipedia describes them this way. On the “standard” or FIA (Footwear Industries of America) scale, women’s sizes are men’s sizes plus 1. On the “common” scale, women’s sizes are men’s plus 1.5. Since US men’s sizes sit one size above UK sizes, that works out to:
- Standard (FIA) scale: US women’s = UK + 2
- Common scale: US women’s = UK + 2.5
The half-size gap is about 4.2 mm. That sounds small, but it is the difference between a chart that calls a 237 mm foot a US 7 and one that calls it a US 7.5. The same article notes that many US makers use offsets larger than the nominal ones, so a brand chart is the final word for that brand.
A quick way to tell which scale a chart uses is to find UK 5 on it. If the US women’s column says 7, it is the standard scale. If it says 7.5, it is the common scale.
Why two EU 38s can fit differently
The EU number describes the last, and the gap between last and foot is a design choice. Wikipedia lists “different allowances” and different “wiggle room” for different shoe types among the reasons size tables from shoemakers and stores disagree. A pointed pump and a hiking boot can be built on lasts with different amounts of toe room, and both can be honestly labeled 38.
Rounding adds a second layer. A US half size is about 4.2 mm and an EU step is about 6.7 mm, so two neighboring US half sizes can round to the same EU number, while the next half size jumps a full EU step. A chart that prints only whole EU sizes has to pick one of the two neighbors, and different charts pick differently.
What ISO 19407 settles, and what it does not
The international standard on this question is ISO 19407:2023, “Footwear — Sizing — Conversion of sizing systems,” which replaced the 2015 technical specification ISO/TS 19407. Its scope says it provides three conversion tables covering the major systems: Mondopoint, European and UK, plus China, Japan, Korea and the US. The published abstract describes the tables as based on foot length, and lists an adult technical conversion table, an adult recommended size-marking table and a children’s table.
The standard is unusually frank about its limits. A note in the scope says the systems were developed and interpreted differently over many years without being formalized, and that “Tables 1 and 2 provide a guideline which can benefit the consumer.” Tables 1 and 2 are the adult tables. In other words, even the ISO conversion is a guideline for adults, not a promise that a given pair will fit.
The full ISO tables are sold, not published free. The converter on this site uses the published foot-length formulas instead and labels its results as guideline conversions. Our data and methods page explains the inputs.
Our formulas, worked out
These are the formulas behind our size converter, starting from foot length L in millimetres:
- UK = 3 × L / 25.4 − 23
- US women’s (standard scale) = UK + 2; common scale = UK + 2.5
- EU = 0.15 × L + 2, rounded to the nearest half size
- Japan = L in centimetres, rounded to the nearest 0.5
We ran them for five whole sizes. Foot length is the computed length for that size, before rounding.
| US women’s (standard) | UK | Foot length | EU / Japan |
|---|---|---|---|
| 5 | 3 | 220 mm (8.67 in) | 35 / 22 |
| 6 | 4 | 229 mm (9.00 in) | 36.5 / 23 |
| 7 | 5 | 237 mm (9.33 in) | 37.5 / 23.5 |
| 8 | 6 | 246 mm (9.67 in) | 39 / 24.5 |
| 9 | 7 | 254 mm (10.00 in) | 40 / 25.5 |
Read across any row and the EU and Japanese numbers move in uneven jumps: EU goes 35, 36.5, 37.5, 39, 40 for even one-size US steps. That is the 8.47 mm versus 6.67 mm mismatch showing up after rounding. On the common scale, every US number in the first column would be half a size higher for the same foot: the 237 mm foot would be labeled US 7.5.
Sizes in recall notices
Size systems also matter when you check a recall. CPSC notices print sizes the way the firm sold them, and that is not always in women’s sizes. The 2017 recall of ACE work boots by Shoes for Crews lists one style as “Unisex in the following men sizes: 4.5 - 11.5, 12, 13, 14, 15 and 16.” A woman who wears a US women’s 7 on the standard scale wears about a men’s 6, inside that range. You can read the full entry on our ACE work boots recall page, and other safety-toe recalls are listed under work boots.
Before you order an imported pair
Start from a measured foot length in millimetres rather than from the number on your current shoes, since that number already carries one brand’s allowance. Our guide on how to measure your feet at home covers the measuring itself. Then:
- Find which US scale the seller’s chart uses by checking what it lists next to UK 5.
- Compare your foot length with the chart’s foot-length or insole column if it has one. A chart that shows only labels, no millimetres, gives you less to go on.
- Expect the EU number to differ by a half size between brands, for the allowance and rounding reasons above.
- Treat any conversion, ours included, as a starting point. ISO itself calls its adult tables a guideline.