What's 'normal' when it comes to penis size?

(Reuters Health) - Are you self-conscious about your penis size? Odds are you don't need to be, but now there's a chart of what's "normal," just in case.

This may be the most accurate estimate so far, according to Dr. Gordon Muir of King's College Hospital NHS Foundation Trust in London, coauthor of the new study.

Muir and his coauthors set out to create "nomograms" of flaccid and erect penis size measurements, excluding men with erectile dysfunction, past surgery or abnormalities.

"The data comes from a very large number of men from the best existing studies," Muir told Reuters Health by email. "We are particularly aware that many men with normal penis size can feel inadequate or ashamed, and this paper should allow specialists to reassure them."

"We also hope that men may be spared unnecessary and harmful surgery, which some less reputable surgeons still promote," he added.

Using more than 20,000 measurements of flaccid length, stretched length, erect length and flaccid and erect circumference, collected by health professionals for other studies, the researchers plotted the distribution of measurements to find the average.

The average flaccid penis was 3.58 inches long (about 9 cm) and 3.66 inches in girth, while the average erect penis was 5.16 inches long (about 13 cm) and 4.59 inches in circumference (about 11.7 cm), according to results in BJU International. Stretched flaccid length was often very similar to erect length, the authors found, which may be good news for men and their doctors since clinical measurements of the erect penis may not be necessary.

Comparing these measures to other physical qualities, like age, body mass index or foot size, the authors found little or no association. Erect penis length and overall height did seem to be related at least somewhat, however - taller men had longer penises.

"There is not a 'right' penis size for a man of any height, just a range of 'normal,'" Muir said. "A bit like shoe size, really!"

As far as how one man compares to another, according to the distribution graphs the authors plotted, men in the 90th percentile for erect length were upwards of 5.9 inches long (about 15 cm), and some of the longest penises in the study were more than seven inches long erect (about 18 cm).

Technically, less than 1 percent of the male population has a "micropenis," which in this group included men with flaccid length below 2.04 inches (about 5 cm). Other researchers have suggested that the smallest 2.2 percent of the population should be eligible for penile augmentation surgery, which would include those with flaccid length up to 2.36 inches (about 6 cm).

But defining "too big" or "too small" still hasn't been firmly nailed down, Muir said.

"Many men with a 9 cm (3.54 inch) erection will have no problems having mutually satisfactory sexual relations, and few men with a longer than average penis seek medical help," he said. "And research shows that women are rarely concerned about the penis size of their partner, rating it much less important than many other factors."

Men may suffer psychological harm and relationship difficulties as a result of worrying about their size, and potential surgical "remedies" may be dangerous and are often unsatisfying, he said.

"We hope that these results will be of help to reputable clinicians who can use them to help reassure men with normal penis size they are indeed normal," Muir said. "We also hope that no man will be subject to physical treatment without a clear understanding of where he sits in the normal range."

There has been little to no similar research on discovering the "normal" for female genitalia, including vaginal capacity, he said. According to some studies, women who have reductive labiaplasty may generally be more satisfied than men who have penile enlargement surgery.

SOURCE: BJU International, online March 2, 2015.