How running shoes should fit

The short answer

Fit your running shoes with the socks you actually run in, later in the day when your feet are slightly larger. There should be roughly a thumb's width – about 1 cm – between your longest toe and the front of the shoe.

The heel should not slip when you walk or jog, and the midfoot should feel held without pressure. A shoe that fits everywhere except the toes will cause problems on long runs.

Why sizing up for long runs is usually wrong

Many runners buy a half size up to protect their toes, then find the shoe feels sloppy and their foot slides forward anyway. The better fix is usually the right size with more toe box volume, not a longer shoe.

If your toes hit the front on downhills, check the heel hold first. A secure heel keeps the foot from sliding forward.

Fit is a three-point check: heel locked, midfoot held, toes free.

Width matters more than you think

Shoes are built on lasts, and lasts differ. Two brands' size 10 can feel a full width apart. If you have wide feet or a high instep, look for shoes offered in wide or extra-wide and check availability before you commit.

A too-narrow shoe causes blisters, numbness and black toenails. A too-wide shoe lets the foot slide and can cause the same problems. The fix is the right width, not a tighter lace.

Heel

No slip when walking, jogging or pushing off.

Midfoot

Held, not squeezed; laces adjustable without hotspots.

Toes

Thumb's width in front; room to spread.

Testing at home

Buy from a retailer with a return policy, run indoors for a few minutes, and check the three points. If the shoe fails any of them, exchange it before wearing it outside.

Shoe fit changes as foams pack down and uppers stretch. If a pair that used to fit starts causing blisters after 300 km (185 mi), it is probably wear, not size.

Wide-fit shoes