Gygax used 10' halls and suggests 3 men can fight abreast in such.
I'm tempted to use colorful language but... Gygax was just incorrect on that one. YOu can construct cases where it'll work, but it doesn't generalize.
Below is a man in a 5' square. Imagine lopping 2' off each side of this - you could stand in it, sure, but taking vigorous action with bladed weapons and not lopping your neighbor's head off would be challenging.
Image from: D&D: Have You Ever Wondered What A Five Foot Square Actually Looks Like? - Bell of Lost Souls