You probably think it’s pretty easy to measure a dick. Whip it out. Grab a ruler. Get it hard. Have a look. Men do it all the time, whether out of boredom, curiosity, insecurity, or any number of other motivations. Serious scientists seem to do it all the time as well. Their efforts have generated flashy data on average penis sizes, which many media outlets, educators, and average men take as gospel.
But think for a moment about all the ways you could measure your penis, and you’ll pretty quickly find it’s not as straightforward as it seems. Do you measure from the top or the side of your penis? If your dick is slightly curved, do you use a cloth measuring tape instead of a ruler to account for that? If you have foreskin, do you count that, or just to the end of your glans? If you’ve measured yourself a few times the exact same way, you may also have noticed your figures weren’t always exactly the same. Was that due to human error, or something different about each erection?
Researchers have been picking at these issues for decades, developing varied measurement tactics. But as fourteen respected urologists reported in an academic review of some of these approaches last year, “little data exists on the best technique to measure penile length.” That could be cause for concern, as getting a solid sense of average penis sizes is important for more than just personal interest and comparison. Accurate measures may help us develop better fitting condoms with lower tear rates or help men with severe, at times debilitating, senses of inadequacy about their own size, among other things. Wildly inaccurate measures could lead to more condom breaks or harm men’s senses of self-worth. So it’s worth taking a look at when, where, and how some of the most common figures on average penis size came from, and understanding exactly how much uncertainty remains today.
Doctors have been trying to gather solid data on average human penile lengths since at least the early 1940s. Perhaps the earliest paper on the subject dates from 1942, when two clinicians in New York measured some 1,500 boys’ and men’s members by stretching them while flaccid and placing a wooden ruler atop them, butted up against their public bones. The thinking at the time was that stretching a flaccid penis offered a fairly reliable proxy of its erect length. These researchers, however, quickly realised that their field needed to address a host of issues, such as how room temperature, and the obvious attendant shrinkage, might play into some of their measurements.
The first study of average penis length to really catch on with other researchers and the public, though, came from the veritable father of sexual research, Alfred Kinsey, based on research from 1948. Kinsey’s research concluded that the average erect male was about 6.21 inches long. “And because he asserted [his] expertise of science in sexual matters,” notes Alicia Walker, a sociologist who has explored the relation of penis size to male self-perception, “others assumed he really did know” the best way to do this research. So his figures and techniques stuck around for some time.
In truth, though, Kinsey used exceptionally shoddy research methodologies. He sent out around 18,000 cards to mostly white and college-aged men and asked them to measure themselves, then send the cards back with data. Only some 3,500 replied. And the figures they reported have been half-an-inch to an inch longer than many subsequent clinically measured studies, as often happens when you ask people to measure their dick and just tell you about it. This may come down to a bias in which only above-average men reply to free-range self-reporting requests, wilful lies, or just inconsistent measurement techniques, some of which can have big consequences.
Thanks to Kinsey’s influence and generally lingering questions about methodology, length data was a little spotty throughout the mid-20th century. In fact, Gordon Muir, a urological surgeon who worked on some of the larger and more influential studies on penile length in recent years, contends that “all the data gathered before 1980” on this subject “is completely unreliable.”
For the most part, researchers since Kinsey have acknowledged the value of getting measurements done by professionals in a clinical setting to avoid the flaws of self-reporting. However, as Walker notes, “having participants come into a physical site to be measured can produce performance anxiety,” making it hard for many of them to get and maintain an erection while being measured.
A few studies have tried to solve this problem by injecting fluids into a flaccid penis, artificially hardening it in the lab. However, says sex researcher Nicole Prause, such shots affect “their targets so well that it is quite likely the ‘full’ erection” they bring about “could be more rigid or slightly larger than a naturally-occurring erection,” giving a false sense of real-world averages.
More often than not, though, researchers have turned back to the 1942 methodology of having a clinician stretch a flaccid penis, measuring it with a ruler laid atop it and jammed down through the pubic fat towards the pelvic bone. (This jamming emerged gradually as the best way to control for variable body fat levels, which can make penises of exactly the same anatomical size seem larger or smaller.) This was the gold standard Muir and three of his colleagues used in their seminal 2015 review of previous clinical studies. That study, which identified 20 previous studies that met its criteria and ended up using data from 15,521 men, aged at least 17, with healthy penises, concluded that the average dick is 5.16 inches long, and 68 percent are 4.5 to 5.8 inches.
Despite the impression some media reports give, though, this 2015 study was hardly the perfection of a viable technique, yielding guaranteed accurate results. Critics note that few studies use the same process to stretch a flaccid penis; some stretch more times than others, which may affect length. Even those that use the same methodology may see differences based on the subjective force a clinician uses to stretch the penis. (Prause notes that many studies just use terms like stretch until resistance or before discomfort.) Predictably, then, several studies have noted disconnects between measurements of the same penis when it is flaccid and stretched and when it is erect.
Jamming a ruler down to the pubic bone is not easy to replicate either. As Muir notes, larger men asked to push the ruler down on themselves often don’t push hard enough to negate their fat. “We’ve tried to standardise the technique used,” Muir says. But “we’re not there yet.”
Even if one could perfect this technique, reliably stretching every penis and jamming every pubis with equal force in a way that reliably predicted a man’s average erect length, this methodology has its limits. It can’t account for extra length hidden in a curved penis. And it can’t account for selection bias in the type of men recruited or volunteering for clinical measurements. Muir and company expressly note that they had little data on non-Caucasian or Middle Eastern men, making it hard to be sure that they’d captured a truly global penile average versus a Euro-centric one.
Seeking to get a better sense of natural erections, and possibly pull a wider field of subjects than expensive and geographically constricted clinical studies permit, at least some researchers have opted for self-reporting that tries to control for the kind of overstatements Kinsey and company seemingly allowed to proliferate in their data. Deborah Herbenick, a sexuality researcher at the Kinsey Institute, and a few of her colleagues published a notable paper in 2014 based on 1,661 self-measurements. Pulled from a larger study on condom fit, Herbenick dangled the promise of help finding a better condom fit and required photo verification of measurements to ensure her self-measures were accurate. She found an average penile length of 5.7 inches along the way.
However Herbenick’s study revealed yet another wrinkle for researchers. She believes her team was the first to explore how the mode of arousal influences the size of an erection. “Men who reported receiving oral sex in order to get their erection for measurement,” she says, “had a longer measurement” on average than men who stimulated themselves. This raises all new questions of how researchers can find a real average, when so many different types of manipulation might yield perceptibly different types and lengths of erections within the same penis, even in the same day.
Ultimately, in Prause’s opinion, “there are no studies that have measured the naturally erect male penis. So we really don’t know what the average size” of a truly wild, representative erect dick is.
Researchers like Prause are still dreaming up new ways of taking penile measurements. She muses about using 3-D imaging or thermography machines for more accurate readings, to be conducted perhaps while a subject watches an erotic film in isolation to get naturally aroused. That plan might provide a more reliable measurement—of girth as well, metrics for which have been far less studied or debated. But it would likely do little to tackle sample size and composition issues that plague measurement studies, or the issue of unclear turgidity differences across time and stimuli. It is hard to envision a practical study that could tackle all of the complications of dick measurement.
But as Herbenick notes, this isn’t a hot topic, or even a notable concern for many people who study human sexuality. Muir argues that the data from existing studies that have followed the best practices for measurement available are converging around a mean. The precision of this mean is not satisfactory for everyone. Walker believes that studies currently put the average erect penis size somewhere between 5 and 5.6 inches. The variability in this range, she argues, limits its usefulness.
But if one is just looking to assure a man that he’s around an average size range, or improve elastic condom fits, it’s not hard to see how a relatively consistent, if broad, ballpark average is useful. And when talking with men suffering from serious dysmorphia, not even the most reliable and proven measure of an average would likely be able to reach them. As Muir says, these people will not believe data that conflicts with their own relentlessly negative view of their own members.
All told, then, the science of measuring penises has come a long way since the uncertainty and poor methodology of the mid-20th century. At the very least, we have a firm grasp on just how difficult calculating such an average is within a population, and how variable penile length may be for an individual. Perhaps scientists will develop new and interesting ways to measure penises, or control for potential biases in their data pools.
But given the complexities we now recognise in this seemingly simple act, no one should hold their breath for truly definitive measurements. And if any man tells you his measurements for some reason, you probably shouldn’t put much stock in them, or compare them to your own. Because if the shortcomings of self-reporting data tell us nothing else, it’s how easily average men can muck up or fudge the seemingly simple task of pressing rulers against their rogers and seeing how the numbers line up against the tip of their heads.
This article originally appeared on Men’s Health