How much room should your foot have in a running shoe?
first you have to determine what type of foot you have ie. flat, high arch, wide, narrow, pronating then find the brand of shoe that fits your foot. for example Brooks and Asics make shoes for wide and/or pronating feet and Nike and Saucony make shoes for narrow feet. i like my shoes to have just enough room to move your toes up and down and side to side. to perfect the fit of your shoe i would suggest orthotics to fit the unique shape of your foot. in the end its all about personal preference. best of luck!
It should fit comfortably. It should not be too tight, just like regular shoes your toes should not touch the end. It can not be too loose so the heal will slip up and down. Some people need a 1/2 size larger running shoe than street shoe. Different brands will be a little different in sizes. Try them on and walk around in the store to make sure if you have not bought this brand or model before.
They need to fit exactly. Too small will not allow for expancion after/during running. Too large will cause blistering. not good eats!!