http://nymag.com/scienceofus/2015/03/here-are-new-numbers-on-average-penis-length.htmlA team of researchers led by David Veale of King's College London Medical School noticed that "there have been no formal systematic reviews of penile size measurements," as they wrote, and they set out to change that. To do so, they collected data from 20 penis-size studies involving 15,521 men, including only those that had at least 50 participants, and in which the measurements were conducted by medical professionals (no self-reporting, for obvious reasons).
Veale and his team's goal was to use this data to develop "nomograms of flaccid and erect penile size measurements" — that is, charts doctors can use to show male patients where on the overall distribution of penis size they sit. Here's what they came up with for length, for example:
It's not necessarily the clearest way to get that information across, especially without someone standing there and explaining it to you, and for Americans, the whole centimeters thing doesn't help. So to simplify things, here are the average sizes the researchers discovered for each category they looked into, translated to inches (don't worry — I didn't round up):
Average length of flaccid penis: 3.61 inches
Average length of flaccid penis stretched out by researchers (yes, that's a thing they do sometimes): 5.21 inches
Average length of erect penis: 5.17 inches (alas, on this most important of categories, the researchers could only find four studies that fit their criteria, so the sample size is a relatively small 692 individuals)
Average circumference of flaccid penis: 3.67 inches
Average circumference of erect penis: 4.59 inches
