Match sizes by foot length (cm), then check model fit — US labels alone can mislead across brands.
Quick answer: On US 10 ≈ Altra US 9.5 (about 27.0 cm).
Full converter (model + shoes you own) · Reverse: Altra → On
Static conversion table (crawlable). Interactive tool above uses the same cm matching.
| On US | cm | Altra US | Altra EU |
|---|---|---|---|
| 6.0 | 23.4 | 6.0 | 38.5 |
| 6.5 | 23.9 | 6.5 | 39.0 |
| 7.0 | 24.4 | 7.0 | 40.0 |
| 7.5 | 24.9 | 7.5 | 40.5 |
| 8.0 | 25.3 | 8.0 | 41.0 |
| 8.5 | 25.8 | 8.5 | 42.0 |
| 9.0 | 26.1 | 9.0 | 42.5 |
| 9.5 | 26.6 | 9.5 | 43.0 |
| 10.0 | 27.0 | 9.5 | 43.0 |
| 10.5 | 27.4 | 10.0 | 44.0 |
| 11.0 | 27.8 | 11.0 | 45.0 |
| 11.5 | 28.3 | 11.5 | 45.5 |
| 12.0 | 28.7 | 12.0 | 46.0 |
| 13.0 | 29.6 | 13.0 | 47.5 |
Even when charts match, lasts differ. Check these guides:
On: Cloudmonster · Cloud 5
Altra: Lone Peak 8
Clothes sizing uses a separate compare path.