Sex Ed

Scientists Measured 15,521 Penises And This Is What They Found

March 6, 2015 by Justin Lehmiller

A recent paper in the British Journal of Urology International reported results from the first systematic review of all penis size studies to date in order to provide a comprehensive look at typical penile dimensions. In total, they reviewed 20 different studies that, combined, included measurements of 15,521 penises from around the world. To be eligible for inclusion, studies had to meet certain criteria. For instance, all measurements had to be performed by a trained health professional (because we know men typically aren’t very honest or accurate when they measure themselves), all participants had to be age 17 or older, and the studies could not be based on samples of men who had complaints about their penis size or functioning. The studies came from a diverse set of countries including Nigeria, Korea, Turkey, India, and Egypt—in fact, only 3 of the samples came from North America. So what did they find?

For the most part, penis sizes appeared to fall within a fairly narrow range. Men in the 50th percentile (i.e., those who were right in the middle of the distribution) had an erect penis length of about 13.1 cm (5.2 inches) and a circumference of 11.6 cm (4.6 inches). For men in the 25th percentile, each dimension was about one centimeter less, whereas for men in the 75th percentile, each dimension was about one centimeter more.

Measurements for flaccid penises told a similar story. Men in the 50th percentile had a flaccid penis length of about 9.2 cm (3.6 inches) and a circumference of 9.3 cm (3.7 inches). Again, the 25th and 75th percentiles were within about a centimeter lower or higher, respectively.

Thus, most men were within just a couple of centimeters of each other with respect to their penile measurements. Extremely small or extremely large penises were uncommon. Just consider this: less than 5% of participants had penises larger than 16 cm (6.3 inches), and less than 5% had penises smaller than 10 cm (3.9 inches).

The researchers also found that, across studies, penis size was either inconsistently or only weakly related to the size of other aspects of the male body, including testicular volume, shoe size, and finger length ratios. Only height had a relatively consistent relation to penis size, such that taller men tended to have longer penises.

Although this paper may represent the most comprehensive look at penis size research to date, it is not without its weaknesses. For one thing, the vast majority of studies included did not obtain measurements of erect penises—instead most studies assessed stretched flaccid penises as a proxy. However, when comparing studies that looked at stretched dimensions to studies that looked at erect dimensions, the researchers found a striking degree of similarity with almost identical results. That said, it is possible that erect measurements obtained in clinical settings are underestimates because it may be difficult for men to become fully aroused in such a situation (indeed, some research has found that when men have a sexual partner help them become erect, their resulting penile measurements are larger compared to guys who become erect through masturbation and fantasy alone).

In addition, although the samples came from a diverse set of countries, most participants were either of European or Middle Eastern descent. Although the researchers did not find evidence of racial differences in penis size in this review of studies, this could be because their data did not allow them the ability to make any definitive comparisons in this regard.

Lastly, we do not know to what extent the men who volunteered to participate in these studies might be different from the rest of the male population. It could be that men who volunteer to have someone measure their penises are different from the rest of the population. One possibility is that perhaps they are more confident in their size than men who opt not to participate.

These limitations aside, the results of this research are still valuable in that they offer the most comprehensive look at the available penis size research to date, which may be reassuring to men who are concerned about their size or who have distorted views of what average is from watching a lot of porn.

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To learn more about this research, see: Veale, D. et al. (in press). Am I normal? A systematic review and construction of nomograms for flaccis and erect penis length and circumference in up to 15,521 men. BJU International.

Image Source: iStockphoto

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Written by
Dr. Justin Lehmiller
Founder & Owner of Sex and Psychology

Dr. Justin Lehmiller is a social psychologist and Research Fellow at The Kinsey Institute. He runs the Sex and Psychology blog and podcast and is author of the popular book Tell Me What You Want. Dr. Lehmiller is an award-winning educator, and a prolific researcher who has published more than 50 academic works.

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