Match sizes by foot length (cm), then check model fit — US labels alone can mislead across brands.
Quick answer: Crocs US 10 ≈ Altra US 10.5 (about 27.5 cm).
Full converter (model + shoes you own) · Reverse: Altra → Crocs
Static conversion table (crawlable). Interactive tool above uses the same cm matching.
| Crocs US | cm | Altra US | Altra EU |
|---|---|---|---|
| 6.0 | 23.9 | 6.5 | 39.0 |
| 6.5 | 24.4 | 7.0 | 40.0 |
| 7.0 | 24.9 | 7.5 | 40.5 |
| 7.5 | 25.4 | 8.0 | 41.0 |
| 8.0 | 25.8 | 8.5 | 42.0 |
| 8.5 | 26.3 | 9.0 | 42.5 |
| 9.0 | 26.6 | 9.5 | 43.0 |
| 9.5 | 27.1 | 10.0 | 44.0 |
| 10.0 | 27.5 | 10.5 | 44.5 |
| 10.5 | 27.9 | 11.0 | 45.0 |
| 11.0 | 28.3 | 11.5 | 45.5 |
| 11.5 | 28.8 | 12.0 | 46.0 |
| 12.0 | 29.2 | 12.0 | 46.0 |
| 13.0 | 30.1 | 13.0 | 47.5 |
Even when charts match, lasts differ. Check these guides:
Crocs: Classic Clog · Echo Clog
Altra: Lone Peak 8
Clothes sizing uses a separate compare path.