The British Journal of Urology set out to stroke egos and calm men's minds by getting the definitive hard (and not so hard) facts about penis size. Dr. David Veale wanted to throw out previous studies, because he said that most of the 96 published papers were done by firms in the erectile dysfunction field.

The BJU wanted a healthy penis sample from across the globe, from a large swath of height, ages, and diet. And the magic numbers from 15,521 studied men is: 3.6" inches flaccid, 5.16" inches erect, and—they stress most importantly—average girth  circumference is 4.5."

The head author of the study, Dr. Veale, found that only 55%of men are satisfied with their penis length, but that 85% of women are satisfied with their partner's size. Veale adds that men have a warped view of what normal is, and this has led to totally unnecessary anxiety. 

Veale's study also reiterates that—while men worry too much about length—female studies have already proven that the most important size in heterosexual activity is girth, because the vaginal wall is the most sensitive area. So, gents, when you get out your ruler, Circumference = π × diameter = 2 × π × radius. Rest cocksure.