Penis Size And Race. Penis enlargement surgery can increase the girth or the non-erect length of your penis on average approximately sucioent.com erect length of your penis will also increase, but usually to a lesser extent. The average size at the beginning of puberty is 6 cm ( in) with adult size reached about 5 years later. Are You an Average Man? Does watching television make you feel like the Danny Devito of the male world? Here are the real stats of the average American man.