ASICS to Birkenstock shoe size
The short answer
ASICS 4 is Birkenstock 35 by the two brands' own charts.
At least one of the two brands publishes no foot length, so the rows line up the US size both charts print. Treat it as the label conversion, not a fit.
| ASICS | ASICS builds it for | Birkenstock, by chart | Same label | Birkenstock builds it for | Birkenstock also prints |
|---|---|---|---|---|---|
| 4 | foot length 21.5 cm | 35 | not published | not published | not published |
| 4.5 | foot length 22 cm | 35 | not published | not published | not published |
| 5 | foot length 22.5 cm | 36 | not published | not published | not published |
| 5.5 | foot length 22.8 cm | 36 | not published | not published | not published |
| 6 | foot length 23 cm | 37 | not published | not published | not published |
| 6.5 | foot length 23.5 cm | 37 | not published | not published | not published |
| 7 | foot length 24 cm | 38 | not published | not published | not published |
| 7.5 | foot length 24.5 cm | 38 | not published | not published | not published |
| 8 | foot length 25 cm | 39 | not published | not published | not published |
| 8.5 | foot length 25.5 cm | 39 | not published | not published | not published |
| 9 | foot length 25.8 cm | 40 | not published | not published | not published |
| 9.5 | foot length 26 cm | 40 | not published | not published | not published |
| 10 | foot length 26.5 cm | 41 | not published | not published | not published |
| 10.5 | foot length 27 cm | 41 | not published | not published | not published |
| 11 | foot length 27.5 cm | 42 | not published | not published | not published |
| 11.5 | foot length 28 cm | 42 | not published | not published | not published |
| 12 | foot length 28.5 cm | 43 | not published | not published | not published |
| 12.5 | foot length 28.8 cm | 43 | not published | not published | not published |
| 13 | foot length 29 cm | 44 | not published | not published | not published |
What wearers say
Charts describe a garment. People who own both brands describe a fit, and their answer ranks above this table once five of them stand behind it. Pick your size in the converter to see whether there are enough yet.
Sources
- ASICS size guide, read on 2026-09-17. ASICS on TrueToSize
- Birkenstock size guide, read on 2026-09-18.