The #1 Rule: Running Shoes Should Be Bigger
Your running shoe should be half a size to one full size larger than your casual shoe. Here's why:
- Foot swelling — feet expand 3-8% during a run
- Toe splay — toes spread on impact and need room
- Downhill protection — prevents black toenails from toes hitting the front
Rule of thumb: There should be a thumb's width (~10mm) between your longest toe and the front of the shoe.
Running Shoe Size Comparison (27.0 cm Foot)
| Brand | US Size | EU Size | Fit Notes |
|---|---|---|---|
| Nike | US 9 | EU 42.5 | Slightly narrow, consider 9.5 for wide feet |
| Hoka | US 9 | EU 42.7 | Roomy toe box, true to size |
| Brooks | US 9 | EU 42.5 | True to size, wide options available |
| ASICS | US 9 | EU 42.5 | Slightly narrow, wide (2E) recommended for >100mm width |
| New Balance | US 9 | EU 42.5 | Most width options: D, 2E, 4E, 6E |
| Saucony | US 9 | EU 42.5 | True to size, good for neutral arches |
| On Running | US 9 | EU 42.5 | Runs slightly short — size up if between sizes |
| Salomon | US 9 | EU 42.7 | Snug performance fit, size up for comfort |
Get Your Running Size
Enter your foot measurement and see your exact running shoe size across all brands.
Find My Running Size →How to Size Running Shoes Correctly
- Measure your feet in the evening — they're at their largest after a day of activity.
- Wear your running socks while trying on shoes.
- Add 5-10mm to your measurement — this is the "running room."
- Measure both feet — always use the larger one.
- Test on a run, not a walk — a shoe that fits standing may not fit running.
When to Replace Running Shoes
Running shoes lose cushioning after 500-800 km (300-500 miles). Signs it's time:
- Outsole is worn smooth
- Midsole creases don't bounce back
- New aches or pains after runs
- Shoe feels "flat" or less bouncy