If a size 9 fits perfectly at one store and feels too small at another, the problem usually isn't your feet — it's that US, EU, and UK shoe sizes are three different measurement systems that happen to share small numbers. Here's how to convert between them, measure your foot correctly, and handle the sizes that fall in between.
Why US, EU, and UK sizes don't line up
Quick answer EU sizing is a single gender-neutral scale based on foot length in centimeters (the Paris-point system), while the US runs separate men's and women's scales — for the same foot, the women's US number is typically 1.5 to 2 sizes larger than the men's number. UK sizing tracks closely with men's US sizing.
It helps to remember that EU is the odd one out in a useful way: it's the only system tied directly to physical foot length, so an EU 42 means roughly the same thing whether it's stamped inside a men's sneaker or a women's boot. US and UK sizing, by contrast, were built around separate men's and women's numbering, which is exactly why a "size 9" can mean different things depending on which section of the store you're standing in.
A rough example (illustrative, not a substitute for a brand's own chart): a men's US 9 shoe is about EU 42.5 and UK 8.5. The same physical foot length in a women's shoe would be labeled closer to a US 10.5.
Example conversions (men's sizing) — illustrative reference values
| US (men's) | EU | UK | Foot length (cm) |
|---|
| 8 | 41 | 7.5 | 26.0 |
| 9 | 42.5 | 8.5 | 27.0 |
| 10 | 44 | 9.5 | 27.9 |
| 11 | 45 | 10.5 | 28.8 |
As a rule of thumb: EU size ≈ foot length (cm) × 1.5 + 2, and men's UK size ≈ men's US size − 0.5. These formulas get you close, but the fastest and most reliable way to check any specific pair is to plug a size you already know into a converter and see every system update at once.
How to measure your foot length at home
Quick answer Measure in the evening with a thin sock on, stand on a sheet of paper with your full weight, mark the back of your heel and the tip of your longest toe, then measure the distance between the marks in centimeters — use the larger of your two feet.
Feet swell over the course of a day, so a morning measurement can run a few millimeters smaller than an evening one — measuring later in the day gives a more realistic result for all-day comfort. Place a sheet of paper against a wall on a hard floor, stand on it normally, and have someone (or you, carefully) mark the heel and longest toe with a pen held straight up and down, not at an angle.
Key fact: Most people have one foot slightly larger than the other. Always measure both feet and size for the larger one — a shoe that's a touch roomy on one foot is far more comfortable than one that's tight on the other.
Once you have the centimeter measurement, it maps directly onto a size chart: 27.0 cm lands close to a men's US 9, for instance. If you'd rather skip the arithmetic, entering the foot-length value into a converter's lookup field returns the nearest US, EU, and UK size automatically, along with the equivalent JP (Mondopoint) size used by many Asian brands.
What to do when your size falls between two numbers
Quick answer When in between, sizing up is usually the safer default — especially for wide feet or thicker socks — while sizing down can suit a snugger, athletic fit for narrow-to-average feet. Always double-check against the specific brand's own chart, since fit varies by shoe last.
A converted size is a strong starting point, not a guarantee, because every brand builds shoes on its own last (the mold a shoe is shaped around). Two pairs labeled the same "EU 42" from two different brands can differ by close to half a size in actual internal length. Running shoes in particular tend to run large by design, to leave room for foot swelling on long runs, while some dress shoe brands are cut narrower and truer to the labeled size.
Example scenario (hypothetical): say your measured foot length converts to a men's US 9.5, but a brand's own size guide lists that specific shoe as "runs small." In that case, ordering the next size up (US 10) based on the brand's own notes is a reasonable adjustment — the general conversion chart gets you in the right neighborhood, but the brand's own guidance should have the final say.
Kids' sizes: age vs. foot length
Quick answer Kids' shoe sizes are based on foot length, not age — age charts are only a rough starting guide, since children of the same age can differ by several centimeters in foot length, especially during growth spurts.
It's tempting to buy shoes by a child's age because that's how clothing sizes are often marketed, but foot growth doesn't track age nearly as tightly as height or weight does. Two five-year-olds can easily be a full size or more apart. Measuring a child's current foot length (using the same paper-and-pen method described above) and matching it to a kids' size chart is far more reliable than guessing from age alone, and it's worth re-measuring every couple of months during active growth periods.
Frequently asked questions
What is EU 40 in US sizes?
In men's sizing, EU 40 is about US 7 (UK 6.5, roughly 25 cm). In women's sizing, the same physical length is about US 9 (UK 7, roughly 25.1 cm) — the two scales differ by about two sizes for an equivalent foot.
How do men's and women's US shoe sizes compare?
For the same physical foot, the women's US number is typically 1.5 to 2 sizes larger than the men's US number (rule of thumb: men's size is about women's size minus 1.5 to 2). For example, a women's US 8 is roughly equivalent to a men's US 6.5, and both are about EU 38.5-39 — useful to know when shopping for unisex sneakers.
How do I measure my foot length at home?
Measure in the evening (feet swell during the day) wearing a thin sock. Stand on a sheet of paper against a wall with your full weight on that foot, then mark the back of your heel and the tip of your longest toe. Measure the distance between the marks to the nearest millimeter, measure both feet, and use the larger measurement. Enter that value in centimeters into the Foot length field above.
My foot falls between two sizes — which one should I pick?
If your foot length falls between two sizes, the larger size is usually the safer choice, especially if your foot is wide or you plan to wear thicker socks. The smaller size can work for a snugger, athletic fit if your foot is narrow to average width. When in doubt, check the specific brand's own size chart, since fit varies by the shoe's last (mold).
Do these size charts apply to every brand?
No — these are standard reference charts (based on the Mondopoint/ISO 9407 and Paris-point systems), not brand-specific measurements. Every brand uses its own last (shoe mold), so the same labeled size can fit differently: some brands run about half a size small, others run large. Whenever possible, cross-check the converted size against the brand's own foot-length measurements before buying.