Online Shoppers: Convert EU 40 to US 8/9, Measure 25.5 cm, Check Chart

by YDA UK

EU size 40 converts to roughly US men’s 8 and US women’s 9, based on a foot length of about 255 mm or 10.0 inches. Some retailers list it as 8.5 or 9.5 instead, so always check the product’s own size chart before you order.

TL;DR:

  • EU size 40 generally converts to US men’s 8 and US women’s 9, based on a foot length of about 25.5 centimeters or 10 inches.
  • Retailers often round sizes and add extra room, so a size 40 can be listed as 8.5 or 9.5, making it essential to check the specific shoe chart.
  • Proper measurement involves standing with socks on, measuring the longest foot, and comparing your recorded length to the product-specific size chart.
  • Size inconsistencies between brands can occur because of different internal measurements or rounding practices, so always consult the individual listing’s guide.
  • For the best fit, consider both length and width, measure later in the day, and prefer shoes with larger toe boxes for swelling and foot volume.
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Table of Contents

Compact conversion reference and how to read it

The numbers above come from an ISO-based reference point, but you will see small variations once you start browsing different retailers. Here is the core reference for EU 40:

  • US men’s: approximately 8
  • US women’s: approximately 9
  • Foot length (Mondo/cm): approximately 25.5 cm
  • Foot length (inches): approximately 10.0 in
  • UK equivalent: approximately 6.5 to 7

These figures hold up well against ISO’s standards-based tables, which anchor conversions to foot length rather than a brand’s internal numbering. In practice, though, you will find listings for the same physical shoe size marked as 8.5 or even 9.5 in men’s sizing. This half-size drift happens because brands round foot-length measurements differently when they build their own charts, and some add a little extra room in the last for comfort, then size the shoe down a notch on the label.

Unisex listings add another wrinkle. A unisex size is usually built on the men’s scale, so a unisex 8 tends to match a women’s 9 to 9.5, not a women’s 8. If a listing says “unisex” without clarifying which scale it uses, treat it as men’s sizing until the chart tells you otherwise, and measure your foot in centimetres so you are not guessing.

How to measure your foot and translate the measurement to the conversion

A good measurement at home takes five minutes and saves you a return shipment later. Follow these steps:

  1. Place a sheet of paper on a hard floor against a wall.
  2. Stand on the paper with your heel touching the wall, since standing spreads your foot slightly wider and longer than sitting.
  3. Measure both feet. Most people have one foot that is slightly longer than the other.
  4. Mark the tip of your longest toe and note which foot that was.
  5. Wear the socks you intend to use with the shoe when you measure, since sock thickness changes the fit.
  6. Measure the distance from wall to toe mark in centimetres and in inches.
  7. Compare that number against the product’s own chart rather than a generic conversion table.

AAOS recommends leaving about half an inch, or 12 millimetres, between your longest toe and the end of the shoe. That gap matters because feet swell during the day and expand slightly during walking or running, so a shoe that fits snugly in the morning can feel tight by evening.

Pro Tip: Measure your feet later in the day when they are at their largest, and if a shoe feels tight across the width rather than the length, look for a wider last instead of sizing up.

Why charts disagree: ISO/standards versus retailer conventions

ISO 19407 states plainly that there is no single perfect conversion between sizing systems. The standard offers compromise tables built around foot length because the historical systems it bridges, including US, UK and EU sizing, were never designed to align with each other.

Retailers add their own layer of variation on top of that:

  • Some brands measure the internal length of the last, not the foot length the ISO tables use.
  • Others round measurements to whichever number looks the cleanest on a size chart.
  • A handful adjust sizing slightly for marketing reasons, making a shoe run noticeably large or small compared with the nominal label.

This is why two pairs labelled “size 40” from different brands can fit differently on the same foot. The practical fix is to treat the ISO figure as your starting point, then let the measured centimetre value and the specific product’s chart make the final call, since standards-based conversion guides are a reference, not a guarantee.

Fit matters: clinical and practical considerations beyond length

Length is only part of the picture. Clinical footwear research finds that mismatches between shoe and foot are common, and that insufficient toe-box depth and internal volume are closely linked to foot pain, a risk that matters more for older adults and people with diabetes. A shoe can match your length conversion exactly and still pinch or rub if the depth or width is wrong for your foot.

AAOS guidance reinforces the toe-gap rule and the advice to measure both feet while accounting for swelling. If you have a wider or higher-volume foot, check the listing for width options or specialist fit notes before assuming a half-size up will solve the problem. It often will not.

Conversion to UK and other international shoe sizes for comparison

EU 40 maps to a UK size of roughly 6.5 to 7, following the same foot-length logic used for the US conversion. The UK scale runs its own separate sequence from US men’s and women’s sizing, which is why a UK 7 does not simply match a US 7.

For quick cross-referencing:

  • EU 40 corresponds to roughly UK 6.5 to 7.
  • The same EU 40 corresponds to US men’s 8 and US women’s 9.
  • Japanese sizing (in centimetres) tends to list the foot length directly, so a 25.5 cm Japanese size lines up closely with the Mondo measurement behind EU 40.

If you are comparing a pair across UK, US and EU listings for the same brand, the centimetre or Mondo figure is the one constant you can rely on. Everything else is a regional label built on top of that same length.

Common brands or shoe types that offer size 40 shoes in US sizing

Size 40 is a widely stocked size across athletic, casual and formal categories, so you are unlikely to struggle finding options. Running and training shoe brands typically list a size 40 as a men’s 8 or women’s 9, consistent with the standards-based reference above. Performance footwear in particular tends to vary more between models within the same brand, since different lasts are built for different movement patterns, so checking the specific model’s chart matters more than usual here.

Formal and dress shoe brands often run slightly narrower and shorter in the toe box than athletic brands at the same nominal size, which is one reason a size 40 dress shoe can feel tighter than a size 40 trainer. Casual and everyday footwear sits somewhere between the two, generally following the ISO reference fairly closely. Across all three categories, the safest approach is the same: measure your foot in centimetres, then check the specific listing’s chart rather than relying on the nominal size alone.

Common brands or shoe types that offer size 40 shoes in US sizing — overview diagram

Tips on dealing with inconsistent sizing across different manufacturers

Inconsistent sizing between brands is common enough that it is worth building a short routine around it rather than hoping for the best each time.

  • Keep a note of your measured foot length in centimetres rather than memorising a single size number.
  • Check the specific brand’s chart every time, even for a brand you have bought before, since lasts change between collections.
  • Read the product description for last width or toe-box notes before ordering.
  • Favour retailers with a clear returns or exchange policy when trying an unfamiliar brand for the first time.

This habit matters more for online purchases than in-store ones, because you cannot try the shoe on before committing. A centimetre measurement travels with you across every brand’s chart, where a size number does not.

Advice on finding size 40 shoes for specific categories like athletic, formal, or casual wear

Athletic shoes built for running or training generally need a touch more depth and a secure heel, so checking for a roomier toe box matters if you have a higher-volume foot. Formal shoes, by contrast, often prioritise a narrower, more tailored last, so if your foot is average to wide, sizing up half a size in dress shoes is common practice rather than a sign you measured wrong.

Casual and everyday shoes tend to be the most forgiving category, generally cut closer to the ISO reference length with a bit of extra room built in. If you are buying across all three categories, do not assume the same nominal size will fit identically in each. Measure once, then check each category’s specific chart before ordering, since a trainer, a dress shoe and a casual slip-on labelled size 40 can fit three different ways on the same foot.

YDA’s point of view: using product charts and YDA Technology to choose the right size

A length conversion gets you close, but the chart on the actual product listing gets you accurate. Certain footwear builders focus on foot-health technology, and the size guidance on each listing reflects the specific last used for that model, not a generic conversion. Measure your foot using the steps above, then match that figure to the chart on the listing rather than the nominal size alone. That one habit prevents most sizing disappointments.

— Panagiotis

Ready to buy: how to order the correct size from Ydauk

Finding the right size 40 equivalent is simpler once you have a measured number in hand rather than a guess based on a label. Ydauk

Here is the short version of the workflow:

  • Measure your longer foot in centimetres, following the steps above.
  • Find the size chart on the specific high performance footwear listing you are considering.
  • Compare your measured centimetre value against that chart rather than the generic US conversion.
  • Check the listing for width or toe-box notes if you have a wider or higher-volume foot.
  • Review the retailer’s return or exchange policy before you order, in case the fit needs adjusting.

Ydauk’s shoe technology is designed to support foot health and comfort alongside accurate sizing, so checking the product chart first gives you the best shot at ordering the right fit the first time.

FAQ

Is size 40 equivalent to size 8?

EU size 40 is commonly listed as a US men’s 8, based on a foot length of about 25.5 centimetres. For women’s sizing, the same EU 40 typically converts to a US 9 rather than an 8.

Is size 40 a 7 or 8?

In US men’s sizing, EU 40 most commonly converts to an 8, not a 7. Some retailers round slightly differently, so checking the specific product’s chart is the safest way to confirm.

Is shoe size 40 a UK 7?

EU 40 generally falls around UK 6.5 to 7, so a UK 7 is a close but not always exact match. The precise fit depends on the brand’s own last and chart.

What is 40 in women’s size?

EU size 40 typically corresponds to a US women’s 9, based on a foot length of roughly 25.5 centimetres. Some retailers list it half a size up or down, so matching your measured foot length to the specific chart gives a more reliable answer.

Sources

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