Previous studies of how women perceive penis size and shape relied on 2D drawings and photographs of flaccid penises. Now, a research team of psychologists from UCLA and the University of New Mexico have taken things into the third dimension.
Reasoning that touch was as important as sight for evaluating a partner's equipment, the researchers printed out a series of vaguely penis-shaped models in blue ABS plastic on a MakerBot 3D printer. (The print files are available here: make your own!) Each of the 33 models represented an erect penis with a unique combination of shape and size, ranging from 4 to 8.5 inches in length and 2.5 to 7 inches in girth.
When the 75 mostly sexually experienced women participating in the study were asked to pick the model they thought matched average erect penis size, most picked a model between 5 and 6 inches in length and between 4 and 5 inches in girth. Not too shabby: the average size of an erect penis reported in the literature is about 5.5 inches in length and about 4.8 inches around.
Whether that's the wisdom of crowds, or whether test subjects were just going for the models in the middle of the offered range isn't entirely clear.
Image from Prause et al. 2015