Match sizes by foot length (cm), then check model fit — US labels alone can mislead across brands.
Quick answer: Merrell US 10 ≈ Altra US 10.0 (about 27.2 cm).
Full converter (model + shoes you own) · Reverse: Altra → Merrell
Static conversion table (crawlable). Interactive tool above uses the same cm matching.
| Merrell US | cm | Altra US | Altra EU |
|---|---|---|---|
| 6.0 | 23.6 | 6.0 | 38.5 |
| 6.5 | 24.1 | 6.5 | 39.0 |
| 7.0 | 24.6 | 7.0 | 40.0 |
| 7.5 | 25.1 | 7.5 | 40.5 |
| 8.0 | 25.4 | 8.0 | 41.0 |
| 8.5 | 25.9 | 8.5 | 42.0 |
| 9.0 | 26.2 | 9.0 | 42.5 |
| 9.5 | 26.8 | 9.5 | 43.0 |
| 10.0 | 27.2 | 10.0 | 44.0 |
| 10.5 | 27.6 | 10.5 | 44.5 |
| 11.0 | 27.9 | 11.0 | 45.0 |
| 11.5 | 28.4 | 11.5 | 45.5 |
| 12.0 | 28.9 | 12.0 | 46.0 |
| 13.0 | 29.8 | 13.0 | 47.5 |
Even when charts match, lasts differ. Check these guides:
Merrell: Moab 3 · Jungle Moc
Altra: Lone Peak 8
Clothes sizing uses a separate compare path.