OK, this is a super geeky post as it is published science. But, there is a lot of discussion on this forum about length and girth. The largest-ever study was just published.
Here is a summary:
http://news.sciencemag.org/biology/2015/03/how-big-average-penis
And the full article (technical):
http://onlinelibrary.wiley.com/doi/10.1111/bju.13010/epdf
Here is a summary:
http://news.sciencemag.org/biology/2015/03/how-big-average-penis
And the full article (technical):
http://onlinelibrary.wiley.com/doi/10.1111/bju.13010/epdf