Sex Ed

Ten Fascinating Facts About The Penis

July 11, 2014 by Justin Lehmiller


The penis is a fascinating piece of human anatomy; however, most of us know surprisingly little about it. So, I decided to compile a list of ten of the most interesting facts about the penis. Do you have other favorite penis facts? Feel free to add them in the comments section below.

1. Men usually get 4-5 erections per night, but it’s not because they constantly dream about sex–rather, this is simply a natural occurrence as guys enter and exit different sleep cycles. This is why men often wake up with “morning wood.”

2. In a study of over 25,000 men, 55% of male participants reported being satisfied with the size of their penis, while 45% wished it was larger and 0.2% wished it was smaller [1].

3. Studies have found that about 1-2% of men report having pierced their genitals. The most common male genital piercing is the Prince Albert.

4. Internally, the human penis is composed of a hydrostatic skeleton. Although this unique type of skeleton doesn’t consist of any bones, this structure still permits the penis to become rigid during an erection. Check out this video to learn more about how erections work.

5. Even though there are no bones in the penis, it is possible to “fracture” an erection. In the U.S., the most common cause of penile fracture is forceful intercourse in which a guy misses his target. Ouch.

6. Contrary to popular belief, penis size is not associated with shoe size. But it is related to a man’s height and weight, such that taller and thinner guys tend to have larger penises (click here to learn more about how penis size is related to other parts of male anatomy).

7. Research has found some support for the idea that there are race-based differences in penis size. Some scientists believe that evolution selected for larger penises in environments where men are in greater competition over female mates. Click here to learn more and to see a worldwide penis size map.

8. Studies find that most heterosexual women report being satisfied with the size of their partners’ penises and that penile length makes no difference in their likelihood of reaching orgasm.

9. A few guys actually have two penises, a rare anatomic variation known as diphallus. Although it is possible for both penises to be similar in size and fully functional, that’s not true in most cases.

10. We do not know definitively what the average penis size is, but studies based on clinical measurements put the average length at 5.1-5.7 inches and the average girth (i.e., circumference) at 4.7-4.8 inches [2]. For a closer look at research on penis size, check out this article.

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[1] Lever, J., Frederick, D. A., & Peplau, L. A. (2006). Does size matter? Men’s and women’s views on penis size across the lifespan. Psychology of Men and Masculinity, 7, 129–143.

[2] Reece, M., & Herbenick, D. (2006). Rates of condom breakage and slippage using a condom fitted to penile length and circumference. European Journal of Sexual Health, 15(S1), 36.

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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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