Running shoes should fit snugly but not tightly, allowing for natural foot movement and swelling during runs. Here are the key points for a proper fit:

• Toe room: There should be about a thumb's or thumbnail's width (roughly half an inch) of space between your longest toe and the front of the shoe to prevent cramping, black toenails, and allow natural toe splay

• Width: The shoe should accommodate the full width of your foot without pinching or pressure points. Your toes should not feel cramped or overlap, and your foot should not spill over the edges of the insole

• Midfoot and heel: The fit should be snug but not tight around the midfoot and heel to lock your foot in place and prevent slipping, but without constricting nerves or blood flow. You should be able to slide a finger between the knot of your laces and your foot

• Size: Running shoes are often recommended to be about half to a full size larger than your casual shoes to account for foot swelling during running and to ensure proper toe room

• Fit check: Try shoes on later in the day when your feet are more swollen, stand and walk around to check for comfort, and ensure no pinching or rubbing occurs on toes, heels, or ankles

In summary, running shoes should feel snug but comfortable, with enough space in the toe box, secure heel and midfoot fit, and slightly larger sizing than everyday shoes to support your feet properly and prevent injury