Also, this is interesting. Via HuffPo:
The smallest erect penis in the study was about 1.6 inches (4 cm) long, and the largest was 10.2 inches (26 cm) long.
The average penile girth was about 4.8 inches (12.2 cm).
Well, that finally settles it. Important observation from Reggie Noble:
My gut says the MEDIAN penis size is slightly smaller though because it's more likely to be over 5.6 by a lot than under by a lot
Also of note:
Moreover, all erections are not created equal, the study also found. Different methods of obtaining an erection may lead to different size measurements — men in the study who became aroused through oral sex reported larger penis size on average than those who attained erections through fantasizing, Herbenick said.
“We don't know if that means that when men have oral sex that it's more arousing and they get a bigger erection, or means that men who have bigger penises could be getting more oral sex in the first place,” Herbenick told LiveScience.
Pic via We Know Memes