No formula converts a US shoe size to an EU one, because the systems were never defined from one another. Each scale grew around different lasts and different reference foot lengths. Our shoe size converter therefore ships lookup tables instead of equations, and matches your input to the nearest table row. That design decision has exact consequences, including one tie-break rule that rounds you down.
What the converter actually contains
Three tables, one per fit track:
- Men: 13 rows, EU 38 through EU 48.
- Women: 11 rows, EU 35 through EU 42.
- Kids: 8 rows, EU 28 through EU 35.
Every row carries four values: EU size, US size, UK size, and foot length in centimeters. Three anchor rows, copied exactly:
| Track | EU | US | UK | CM |
| Men | 44 | 10 | 9 | 28 |
| Women | 38 | 7.5 | 5 | 24.5 |
| Kids | 32 | 1 | 13 | 20 |
The kids row is the one that surprises people. The kids US scale restarts at 1 after 13, which is youth sizing, so a kids EU 32 carries US 1 and UK 13 in the same row.
The matching rule, step by step
1. Read your known size and the system it belongs to: EU, US, UK, or CM.
2. Select the table for the fit track that size belongs to: men, women, or kids.
3. Compute the absolute difference between your input and every row's value in that system's column.
4. Return the row with the smallest difference.
The tie rule hides in step 4. The code replaces the current best row only on a strictly smaller difference, so when two rows tie, the earlier row wins. The earlier row is always the smaller size.
A worked conversion with a tie
Input: US men 7.5.
1. The men's US column contains 7 and 8 in adjacent rows, with EU 40 and EU 41.
2. The differences are 0.5 for the US 7 row and 0.5 for the US 8 row.
3. The tie keeps the earlier row, US 7.
4. Output: EU 40, UK 6, 25 cm.
The consequence is direct. A size 7.5 foot is longer than the 25 cm the row describes, and the converter still hands you the 7 row. When your input lands exactly between rows, do the conversion by centimeter instead: measure the foot and read the CM column, the only column with a physical unit behind it.
Converting by foot length
1. Measure your feet in the evening, when a full day on them has spread them to their largest.
2. Measure both feet from heel to longest toe.
3. Use the larger measurement.
4. Find that centimeter value in your track's table and take the entire row.
The centimeter path skips the tie problem because you compare a measured length to measured lengths, with no national scale in between.
Why men's and women's US numbers differ
The US column is not one scale. The men's table and the women's table each carry their own US column, and the converter switches columns when you switch gender. In our data, US women 7 maps to 24 cm and US men 7 maps to 25 cm, so the same printed number describes feet 1 cm apart. Selecting the wrong track shifts your US result by about 1.5 sizes and silently corrupts every other value in the row.
Where the table ends
The matching loop always returns some row. It starts from the first row and only replaces it on a better match, so an input outside the table's range returns the nearest edge row rather than an error. Concretely:
1. A men's input below EU 38 returns the EU 38 row.
2. A men's input above EU 48 returns the EU 48 row.
3. A women's input above EU 42 returns the EU 42 row.
4. A kids input below EU 28 returns the EU 28 row.
Treat an edge-row result for an out-of-range input as a signal to find a chart that covers your size, because the row's centimeter value no longer describes your foot.
Honest downsides
- No interpolation. Inputs between rows snap, and ties snap down to the smaller size.
- Coverage stops at the table edges listed above, and the tool never says so.
- System equivalence is not brand fit. Two brands use different lasts, and two shoes with the same EU number can differ in width and volume. The row tells you what the systems call your foot, and nothing about a specific shoe.
- The gender control changes which US column is read. One tap in the wrong place moves your converted US size by about 1.5.
- Half sizes outside the table's rows, like men's US 7.5, do not get their own row anywhere in the men's table.
Checklist
- [ ] Measure both feet in centimeters in the evening.
- [ ] Fit to the larger foot.
- [ ] Pick the correct track: men, women, or kids.
- [ ] Prefer the CM column when your input falls between rows or ties.
- [ ] Treat an edge-row result as out of range and find a covering chart.
- [ ] Check the brand's own size guide before ordering.
Measure your feet tonight and run your centimeter value through the [shoe size converter](/en/shoe-size-converter). If a row you rely on disagrees with a brand chart you trust, send both numbers, because the tables only improve when real feet check them.
