Basically a cue is 58 inches, that is about 5 feet. You need that 5 feet on every side of the pool table to be able to stroke a ball on the rail. So add 10 feet to the length and 10 feet to the width, that is the dimensions your room needs to be to fit the pool table, and allow people to shoot on it.
Your table is 5x10, you need a 15x20 room at the least, your table is a 6x12 snooker table, You need 16x22 as a minimum, and so on.