http://men.webmd.com/guide/penis-enl...it-work?page=1

The average erect penis is four to six inches long, with a circumference of four to six inches. There’s more variation in the size of flaccid penises. But that just means that a guy who looks well hung in the locker room isn’t likely to get much bigger when erect; conversely, a guy who looks small will grow a lot.