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On the Matter of SizeThe inexact science of penis measurement.

By Kent Sepkowitz Posted Monday, Feb. 13, 2006, at 5:20 PM ET

Here's a question I bet you can't answer, though the economy of the free world depends on it—you know, rockets, tall buildings, showbiz, oil wells, rifles, professional sports, world wars.

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How long is the average penis?

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As a Valentine's Day gift, I shall solve the mystery.

Outside the pages of unbuttoned magazines and buttoned-down sex surveys, out-loud discussions of size have been avoided for ages. Now, every day we're accosted with the latest technology of penis elongation. Your e-mail, my e-mail, everyone's e-mail is flooded with breathless promises: "You, Rose," one message tells my infant niece, "can have a larger penis using the latest non-surgical advances."

The penis elongation industry has created the need for careful studies to determine who should and should not be considered for "augmentation." Urologists worldwide are busily stretching and measuring and reporting their findings. Most recent articles hail from outside the United States—the Italians, Turks, and Greeks seem especially engaged. There is a fascination with determining the dimensions of newborn boys of different ethnic pedigrees. From Ben-Gurion University in Israel, we have "Clitoral and penile sizes of full term newborns in two different ethnic groups" (Jewish and Bedouin), and from Singapore General Hospital, "Penile length of [Chinese, Malay, and Indian] newborns in Singapore."

The modern story begins in 1942, when American researchers W.A. Schonfeld and G.W. Beebe set out to define normal genital growth and variation in males from birth into their 20s. They measured penis length (using a wooden ruler), circumference (using a series of graded rings), and testis volume (using an instrument called the orchidometer) in 1,500 volunteers of various ages. But it wasn't so easy. And the difficulties that the first wave of researchers encountered continue to render our latter-day interpretation of penis studies a risky business.

First off, what do you measure—from where to where? What configuration should the penis be in—erect or flaccid? What about room temperature? (George Costanza was on firm scientific ground when he lamented the grim reality of shrinkage.) Furthermore, who should do the measuring? Self-reported measurements are more, um, forgiving than size determined by a disinterested medical professional, by half an inch or more. The methodological problem is on display in online penis measurement surveys like altpenis.com (900,000 and counting) or sizesurvey.com. More importantly, it confounds the most frequently quoted study in the field, by Alfred Kinsey. The great sex researcher of the 1950s interviewed 18,000 men, 3,500 of whom mailed back cards on which they recorded their own length and circumference in both erect and flaccid states. (Click here for a recent reanalysis of Kinsey's data that compares the penis length of heterosexuals and homosexuals.)

The 1940s researchers introduced another problem. After much analysis and reanalysis, they concluded that measurement of neither the flaccid nor the erect penis could be reliably reproduced. So, they created a new approach: They measured the flaccid but stretched penis. Although statistically validated and still used in most studies, this method of measurement creates a different conundrum, because the maximally stretched flaccid penis simply does not exist in nature. Outside the doctor's office, no one has ever seen one. Who cares how long the average one is? Plus, the stretch-'em approach has led to some bitterness in the literature, over a study by French researchers who stretched the penises of their subjects three times and reported suspect lengths—on average, more than an inch longer than the rest of the pack. Cheaters.

So, after more than 60 years, and thousands and thousands of penises measured for the cause, we still don't know who should measure, what to measure (erect, flaccid, or stretched), where to measure from (the pelvic bone to the tip of the glans is the usual itinerary, but some researchers push the ruler against the pubic bone to give obese people a break, or don't allow for the gain in length of curvature), or how many measurements are enough to assure an accurate result.

But wait—there's a hidden benefit here. The lack of resolution teaches readers to scrutinize how a study is conducted. The literature on penis size—found in such journals as The Archives of Sexual Behavior, European Urology, and The Journal of Pediatric Endocrinology and Metabolism—makes everyone an expert in methodology. In this field, readers are wired for the slightest perturbation. Once you've become a veteran of the penis-elongation debate (and I invite you to join), you know all about how data can be massaged or manipulated. You'll never again read a Gallup Poll on unemployment stats and accept the findings at face value.

My hope is that the golden age of penis literature will usher in another golden age—with a revenge-of-the-nerds twist—of alertness to the countless nuances embedded in statistics. Roger Maris and his mighty asterisk made us aware that the rate of home runs matters more than the raw number of dingers per season (60 HRs in 154 games trumps 61 in 162 games every time). The field of penis elongation should make us similarly mindful of the limits of selective information.

But in case you're still wondering, here is what we know: When self-measured, the median length of a stretched flaccid penis is about 5.1 inches. For an erect penis, most studies come in at 5.5 to 6 inches. The average flaccid penis is in the 3.5- to 4-inch range. If someone else is doing the measuring, well, the numbers come out lower. But go ahead, add a little extra. After all, it's Valentine's Day.