What is EU 42 in US shoe sizes? 11 brands' official charts disagree

What is EU 42 in US shoe sizes? Most converters give one number with total confidence. I went to the source and read the official size charts from 11 brands, and this is what they print for a men's EU 42:

So there are two right answers. Which one applies depends on the shoe you're buying.

That killed my plan for the shoe size converter on Toggle9. I'd expected to write a conversion function. There's no function to write, so the tool is a lookup across 15 charts with 339 rows, and its answer includes how many charts agree.

This post covers the shortcuts I tested, why they fail, and how the lookup works. The data is public if you'd like to build on it.

One label, nine answers

Run it the other way and it gets worse. Here's what 9 men's charts print for a US men's 9, using one chart per brand:

That's 0.8 cm of disagreement over the same label, from the people who make the shoes.

The shortcuts, tested

Size guides are full of quick rules. I ran the common ones against every chart row that has both columns:

The EU rules are the bad ones, and the reason is in the data. The gap between US and EU isn't constant. On Converse's men's chart, US 6 is EU 38.5, a gap of 32.5. US 23 is EU 62, a gap of 39. A fixed offset can't track a gap that grows, which is why the worst misses are at the big end of the chart.

The women's-to-men's rule looks safest at 84%, but it's a good example of why the 16% matters. A women's 10 is a men's 8.5 on Nike and Vans. On adidas it's a men's 9. If a shoe only comes in men's sizes, that half size depends on the brand.

Three things that make charts hard to compare

EU sizes come in thirds. adidas prints 42⅔. In a JSON file that becomes 42.67, and now === won't find it when somebody types 42 2/3, so lookups need a tolerance:

const close = (a, b, t) => a != null && Math.abs(a - b) <= t;

"Length" doesn't mean one thing. Seven charts say foot length. adidas says heel to toe. Others label the column CM or Length, and three give no length at all. Comparing those columns is fair as "what each chart prints", but you can't call it one measurement. That's why the tool shows the column name beside the number.

US sizes are split by gender, and UK and EU usually aren't. So one UK size has two US answers, and a converter has to ask which US scale you mean.

The lookup

The core is small. Given a label, find it in every chart that carries it, then report the answers with their counts:

function answers(charts, have, value, want) {
  const tally = {};
  for (const chart of charts) {
    const row = chart.rows.find(r => Math.abs((r[have] ?? Infinity) - value) < 0.2);
    if (row && row[want] != null) (tally[row[want]] ||= []).push(chart.brand);
  }
  return Object.entries(tally).sort((a, b) => b[1].length - a[1].length);
}

answers(mensCharts, EU, 42, US_MEN);
// [["8.5", ["adidas", "ASICS", "Converse", "Nike", "Salomon", "Timberland"]],
//  ["9",   ["Clarks", "Skechers", "Vans"]]]

The design decision is in the return value. It's a list, not a number. The page leads with the most common answer because that's what people came for, then shows who says what. If you know the brand, it answers from that brand's chart alone.

Two choices are worth stealing:

• Count each brand once. Nike has a men's and a women's chart that both carry men's sizes. Count both and Nike gets two votes.
• Say "the chart says", never "this will fit". A size chart isn't a fit guarantee, and the tool doesn't pretend it is.

That's also why the tool starts from the foot when it can. You can enter a length in centimetres, or use the printable foot size sheet, and then every label becomes a comparison against one measurement.

What the data doesn't cover

I aimed for about 30 brands and got 11. Several sites gave me nothing readable: Crocs put up a bot challenge, New Balance returned an error page, and Puma, HOKA, Birkenstock and others had no chart I could read. I don't work around blocks, so those brands aren't in the data and I haven't filled the gaps from third-party tables.

Also, ASICS covers men's sizes only and Brooks covers women's only. There's an international standard for this, ISO 19407, but it's paywalled, and I didn't use it. These are brands' published charts, read on 7 November 2026, and any of them can change.

Use the data

Both summary tables are free to download:

• EU to US and UK, every size
• US men's 9 by brand

The shoe size conversion tool runs in your browser and takes EU, US, UK or centimetres, with the brand charts side by side.

Every Toggle9 tool cites its sources and is re-checked on a schedule: how we check our tools explains the tests.

AI assistants helped build the tool and draft this post. The figures come from the test script run on 7 November 2026.