The average erect penis is about 5.5 inches (13.9 cm) long. That number comes from a large meta-analysis published in The Journal of Urology that pooled data from studies across multiple countries. Most men fall within a relatively narrow range, and the actual average is smaller than many people assume.
Average Length and Girth
A systematic review of over 15,000 men found an average erect length of 5.1 inches and an average erect girth (circumference) of 4.5 inches. A separate, larger meta-analysis that included more recent data put the average erect length slightly higher at 5.5 inches (13.93 cm). The difference between these two figures reflects normal variation across study populations and measurement methods, but both land in the same general range.
When flaccid, the average length is about 3.4 to 3.6 inches with a girth of roughly 3.7 inches. Flaccid size varies a lot more than erect size. Some men are “growers,” meaning their penis changes significantly between its soft and hard states, while others are “showers,” staying closer to their erect size when flaccid. Neither pattern is more common or more “normal” than the other.
What the Distribution Looks Like
Penis size follows a bell curve, which means most men cluster close to the average and very few are far above or below it. A major study published in BJU International found that erect length averaged 5.2 inches (13.12 cm) with a standard deviation of about 0.65 inches (1.66 cm). In practical terms, that means roughly two-thirds of men measure between 4.5 and 5.8 inches erect. Only about 5% of men are longer than 6.5 inches, and only about 5% are shorter than 3.9 inches.
This is worth keeping in mind if your frame of reference is pornography, where performers are selected specifically for being far outside the norm. Surveys that rely on self-reporting also tend to skew high, since men often round up. The most reliable studies use measurements taken by clinicians.
How to Measure Accurately
Clinical studies use a standardized method called the “bone-pressed” measurement. You place a ruler or measuring tape along the top of the penis, press the end firmly into the pubic bone at the base (pushing past any fat pad or pubic hair), and measure in a straight line to the tip. Pressing into the pubic bone is important because it accounts for differences in body fat and gives a consistent measurement regardless of weight.
For girth, wrap a flexible measuring tape around the thickest part of the shaft. If your penis has a curve, use a flexible tape rather than a rigid ruler to follow the contour. Avoid measuring in a cold room, since cold temperatures temporarily reduce size.
How Size Changes With Age
Penis size is essentially fixed by the end of puberty, which for most men is the late teens to early twenties. From there, it stays relatively stable for decades. Later in life, though, gradual changes can occur. Reduced blood flow and lower testosterone levels can cause some loss of length, potentially up to an inch over time. A buildup of scar tissue in the erectile chambers can also contribute. Weight gain in the lower abdomen can make the penis appear shorter by burying more of the base under a fat pad, even if the actual tissue hasn’t changed.
Testicle size can also decrease with age, shrinking by as much as a third. These changes are gradual and vary widely from person to person.
Why Perception Often Doesn’t Match Reality
Studies consistently find that a large percentage of men who believe they are below average are, in fact, perfectly average. Part of this comes down to angle: looking down at your own body foreshortens your view, making your penis appear smaller than it would from the side. Comparing yourself to other men in locker rooms isn’t reliable either, since flaccid size is a poor predictor of erect size.
Research on what sexual partners actually prefer also challenges common assumptions. A study in PLOS ONE that asked women to select preferred sizes from 3D-printed models found they chose options close to the statistical average for a long-term partner: about 6.3 inches long and 4.8 inches in girth. For a one-time encounter, the preferred size was only slightly larger. Both figures are close enough to the average that most men fall within a range their partners find satisfactory.
Size anxiety is common, but for the vast majority of men, what they have is well within the normal range. True micropenis, a clinical condition defined as an erect length of 3.67 inches or less, affects fewer than 1% of men.