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 was part of a larger research project dealing with condom fitting. The condom company Richter Rubber Technology of Kedah, Malaysia provided condoms to participants.
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.
Editor's note: This story was updated on July 15 to include mention of the company that provided condoms
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Tia is the managing editor and was previously a senior writer for Live Science. Her work has appeared in Scientific American, Wired.com and other outlets. She holds a master's degree in bioengineering from the University of Washington, a graduate certificate in science writing from UC Santa Cruz and a bachelor's degree in mechanical engineering from the University of Texas at Austin. Tia was part of a team at the Milwaukee Journal Sentinel that published the Empty Cradles series on preterm births, which won multiple awards, including the 2012 Casey Medal for Meritorious Journalism.