I want to discuss human penis sizes. But I’m going to do my best to be dignified about it. I don’t bring it up for its shock value. It is rather that I noticed something that I think is really interesting about the subject. It all started with an Aaron Carroll post over at The Incidental Economist, Penis Size and Suicide: Two Unrelated Stories. The news about penis sizes is from a research paper in BJUI, Am I Normal? A Systematic Review and Construction of Nomograms for Flaccid and Erect Penis Length and Circumference in Up to 15,521 Men. The remarkable thing is just how unremarkable human penises are.

Let’s start with the facts. The length of erect penises are 5.17 ± 0.65 inches. The circumference of erect penises are 4.59 ± 0.43 inches. What’s interesting here is not the lengths but rather the standard deviations. What we know about a normal distribution is that 95% of all individuals will fall within plus or minus two standard deviations. So 95% of all men have penis lengths between roughly 3.9 and 6.5 inches. If you want to get way out into the weeds of pretty much everyone you’ve ever known, 99.7% of all men have penis lengths between roughly 3.2 and 7.1 inches. The girth of penises is even more constrained: 3.3 and 5.9 inches.

Now you may be wondering where Jonah Falcon fits into all of this. He apparently has a 13.5 inch long penis. Sadly, I have no data on the circumference. But 13.5 inches represents a staggering 13 standard deviations from average. To give you so idea of just how outrageous that is, seven standard deviations represent a one in 400 billion chance. And why did I quote seven and not 13? Because the error function failed in OpenOffice after seven. So basically, the odds are astronomically small.

Does that mean that the statistics from the study are wrong? No. It means that statistics just aren’t that useful when you get way out on the tail of a function. The numbers are probably about right. And what this means is that our general mythology of the penis is wrong. I’m glad to hear that. I wish we would stop mythologizing the penis altogether. I don’t think it is just a sign of my heterosexuality that I think the penis is kind of creepy. But it reminds of a joke by a female comedian decades ago, who said that of course women were bad at math because men were always telling them that this (she indicated about three inches with her fingers) was eight inches. There is undoubtedly much truth to that.

But just as the man with an eight inch penis seems to be mostly a myth (especially if he announces it), so is the idea that women don’t care about penis sizes. According to a study out of UCLA, in one-time sexual encounters, women prefer men with penis of greater girth. For long term relationships, they seem to care more about men with jobs. Be that as it may, you can read all about why this would be (it ain’t complicated) at Medical Daily, What Women Want: Penis Size Matters for One-Night Stands, but Not Long-Term Relationships.

So there you have it: all the statistics you ever wanted to have about penis sizes. As for me, I’m just glad I don’t have to strap my penis down before I go out like Jonah Falcon does. I consider it enough of a nuisance as is.