The average American man's penis is 5.6 inches (14.2 centimeters) long when erect, a new survey of 1,661 men finds.
The study, published online July 10 in the Journal of Sexual Medicine, is relatively consistent with the results of prior surveys of penis size.
Penis size has been the subject of dozens of studies, as well as countless urban legends, myths and spam emails. For many men, the idea of not measuring up can cause a great deal of anxiety.
But whether penis size truly matters to a man's sex partner is up for debate. Some research shows that women who experience vaginal orgasms do so more consistently with men of bigger girth. [Macho Man: 10 Wild Facts About His Body]
In the new study, Debby Herbenick, a researcher at Indiana University, and her colleagues asked 1,661 men to measure their penis's length and girth for the purposes of fitting for a condom. (The men submitted their data online.) At the time of their measurement, some men were with partners or "a friend," although most employed a DIY method for attaining an erection.
Not surprisingly, penises come in all shapes and sizes. The smallest erect penis in the study was about 1.6 inches (4 cm) long, and the largest was 10.2 inches (26 cm) long.
The average penile girth was about 4.8 inches (12.2 cm).
Moreover, all erections are not created equal, the study also found. Different methods of obtaining an erection may lead to different size measurements — men in the study who became aroused through oral sex reported larger penis size on average than those who attained erections through fantasizing, Herbenick said.
"We don't know if that means that when men have oral sex that it's more arousing and they get a bigger erection, or means that men who have bigger penises could be getting more oral sex in the first place," Herbenick told LiveScience.
The study found that other characteristics of a man, such as his race or orientation, weren't good predictors of his member's size.
Male penis size is well-charted terrain in studies, Herbenick said. Now, she'd like to gather data on female genitalia.
"It would be good for women to have good data to show, 'Hey, there's a lot of diversity for women's genitals, just like there are for men's," Herbenick said.
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Southern Right Whale
The ginormous testicles of right whales actually rival those of blue whales, and are among the largest of any animal. This video shows a rare Southern Right Whale mating group.
Alligators sport permanently erect penises, according to recent research. Here is video of a dissected alligator's penis that snaps into mating position when the pelvic nerve is tugged.
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Relative to body size, barnacles have the longest penis of any animals. Here, a video shows the penis in action.
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Mating is painful for female cats. It's not the biting that hurts -- it's the male's penis, which has over 100 tiny barbs. Here is video of how a cat's barbed penis works.
The equivalent of a penis in snakes and lizards is the hemipenis, which is kept inverted within the body until needed. Here's the hemipenis of a crested gecko (<em>Rhacodactylus ciliatus</em>), which hails from southern New Caledonia, an archipelago in the Pacific Ocean.
The penis of an orb-web spider detaches after sex. Here's a view of the detachable penis (left); a male without one is on the right.
With all those violent-looking spikes, the penis of <em>Callosobruchus maculatus</em>, or Bruchid beetle, is pretty scary. Here's a close-up look.
The penis of the freshwater <em>Gambusia quadruncus</em>, also known as a Llanos Mosquitofish, has four hooks with which to grab females. Here's a magnified view of the genitalia.