The average length of an erect penis is 5.16 inches (13.12 centimeters) and the average circumference is 4.59 inches (11.66 centimeters), according to a new analysis of penis length studies involving more than 15,000 men around the world.
http://onlinelibrary.wiley.com/doi/10.1111/bju.13010/epdf
via Average Penis Size Study Shows ‘Normal’ Isn’t Necessarily What You Thought.