Study: The typical erect penis is 5.1 inches

Men worry — likely too much — about penis size. Seth Stephens-Davidowitz recently combed through Google search data in an article for the New York Times, and found that for every 100 questions about penises, there were 67 about the heart, 35 about hands, five about the brain, and two about lungs. Many of those questions focused on penis size.

Now researchers in the urology journal BJU International have provided the hardest answer to the question of typical penis size. They have published a meta-analysis of English-language studies measuring the penis size of more than 15,000 men across Asia, Africa, Europe, and the US. The median erect penis length, they find, is 5.1 inches — not six inches, as many think. If someone is above that, he's bigger than most men. If someone is below that, he's smaller than most men.

(BJU International)

Perhaps more interesting is the narrow distribution of erect penis size. Most men are remarkably close to each other: 4.7 inches is in the bottom 25 percent, and 5.6 inches is at the top 25 percent. Very few people — those within the top 1 percent — reach 9 inches.

Researchers only counted studies in which a certain kind of measurement was taken (from the base of the penis to the tip) by health professionals, not self-evaluations. Studies were also excluded if they had any potential bias, such as participants who had some sort of penile abnormality, a complaint about penis size, or erectile dysfunction.

The analysis also found the research is conflicting and mixed on whether penis length correlates with weight, finger length, and foot size, likely indicating that there is no correlation between penis size and those measures. But studies did find a consistent link between penis size and height. Not enough studies met the researchers' standards to gauge how penis size and race correlate.

There are some limitations to the study. It's questionable how reliable measures were across different studies, and how factors like temperature, level of arousal, and time since previous ejaculation affected results. Some participants may have enrolled in the studies because they were confident in their size, skewing the numbers upward. To allow better analyses of the data, the researchers recommend controlling for these issues in future studies.

It's also worth remembering that men seem to be more critical of their own penis size than women. A large internet survey of more than 52,000 heterosexual men and women found 85 percent of women were satisfied with their partner's penis size, but 55 percent of men reported dissatisfaction with their own size. (Such preferences could vary in gay and bisexual communities.)

As health-care researcher Aaron Carroll said on his blog, "Everyone should stop worrying about this. I'd love to stop writing about it."

Further reading: Sex myths: what's real, what's fake, and what still needs more science.

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