Some fun facts here:
http://en.wikipedia.org/wiki/Human_penis_size
Studies show that men have a lot of pride in their penile thing. Women don't share as much in the glorification, though. A small minority do.
A dollar bill is about 6" in length. I looked and it's actually a bit longer than that. But if you wrap that around your meat that's one way to get its circumference. Most males have a circumference about 4.85". The girth curve falls sharply in the 5" to 6" range. So if you're close to filling out the dollar bill then you're in the minority. Scientific measurements average the base, the middle and just below the crown.
Something I saw that was interesting in the wiki link is that humans have the largest genitalia of all primates, both in absolute and relative terms. Wow. I did not know that. Apparently, scientists haven't measured bigfoot, yet. I think bigfoot would have a bigger trophy to flaunt.