Men do lie about the size of their penis, exaggerate length by a fifth - study

Man looking down his pants with a magnifying glass - background: tape measure wrapped around a banana
That old chestnut has now been confirmed by science. Photo credit: Getty Images

It's generally accepted that when it comes to the nether regions, blokes have a habit of telling tall tales - a fact that has now been confirmed by science.

A study conducted by researchers in Denmark found it is a mathematical certainty that men tell porkies about the size of their penis, with the average Joe exaggerating their length by 21 percent, or about a fifth. 

The sly dogs also have a tendency to tell half-truths about their height: according to the study, men will on average add around 2cm to their height, which conveniently, can be the difference between a still respectable five-foot-eleven and the coveted six-foot mark.

In an online survey, 224 Danish men aged 18 to 35 were to asked to self-report "bodily markers that signal physical dominance" - athleticism, height, weight and penis size.

The male participants were split into two groups in order for the researchers to explore whether the amount of monetary reward would influence the quality of the data. One group was paid $5 and the other $22: while those who received greater financial compensation still exaggerated their answers, it was to a lesser extent, the researchers found. 

Of the sample, 26 reported their penis as being more than one-foot long - that's at least 12 inches. One even said his appendage was longer than a half-mile, but we can safely assume he either made a glaring miscalculation, or it was cock-and-bull. 

As part of their research, which was published in the journal Frontiers in Psychology in February, the team compared the average of the data obtained from the survey to the average measurements in Denmark. The researchers' theory was that if every participant answered honestly, the average height, weight and penis size in their population would correspond with the national figures.

When the answers were averaged, it was easy for the researchers to determine that many of the men surveyed had been a little flexible with the truth.

A number of the participants had reported their penis as larger than the claimed, but unverified, world record of 34 cm, or 13 inches. Any clearly falsified answers were removed from the sample to avoid corrupting the dataset.

Researchers also removed any participants from the sample who spent less than 10 minutes or more than four hours taking the survey, noting it gave reason to doubt the validity of their answers. 

The final dataset included 191 men and the results suggested the average flaccid penis was 18.02cm, or 7.1 inches, in length. However, this was 21 percent longer than the Danish average of 14.88cm, or 5.85 inches - giving the researchers reason to conclude a number of participants had boosted their measurements. 

The study also found that men were likely to exaggerate their athletic ability. In the survey, the participants were required to place their athleticism on a scale of one to 10, with the majority ranking their prowess above a five. The researchers deduced that in reality, this was an overestimation of the average score.

Despite having a tendency to exaggerate their height, penis length and fitness level, the study found the participants largely told the truth when it came to their weight. 

"The finding that participants do not seem to have over-reported their weight, but likely exaggerated their height slightly, also implies that they sought to present themselves as more physically fit," study author Jacob Dalgaard Christensen and his colleagues wrote, noting that the men who received a higher monetary payment were more inclined to answer honestly.

The researchers concluded that men should typically not be trusted to accurately self-report information about their bodies, noting that professionals, such as doctors and fellow researchers, should instead be collecting the official measurements. 

"Our results suggest that private data related to bodily cues of masculinity can only be reliably collected in the lab, where conditions can be fully controlled.

"Given our findings, scientific studies with self-report data concerning penis size should be interpreted with great caution."