The average erect penis is 5.16 inches (13.12 cm) long, based on a review of over 15,000 men measured by healthcare professionals. The average erect circumference, or girth, is 4.59 inches (11.66 cm). These numbers come from a widely cited analysis published in BJU International that pooled data from 17 studies across multiple countries, making it the most reliable reference point available.
Average Flaccid and Erect Measurements
Flaccid size varies more than erect size because blood flow, temperature, stress, and physical activity all influence it from moment to moment. The same large dataset found an average flaccid length of 3.6 inches and an average flaccid girth of 3.7 inches. Many men notice significant differences in their flaccid size throughout a single day, which is completely normal.
Erect measurements are far more consistent. Most men fall within a relatively narrow band: roughly 4.7 to 6.3 inches in erect length covers the vast majority of the population. A length of about 6.3 inches hits the 95th percentile in published data, meaning only about 5% of men are longer. The distribution works the same way on the shorter end, with about 5% of men measuring below roughly 4 inches erect.
Why Self-Reported Numbers Run Higher
If the averages above seem lower than what you’ve seen cited elsewhere, measurement method is the main reason. Studies relying on self-reported data consistently produce higher numbers. One self-report survey found an average erect length of 14.49 cm (about 5.7 inches), while clinician-measured studies converge closer to 13 cm. Some self-report samples from Europe have averaged as high as 16.8 cm (6.6 inches), more than an inch above what clinical measurement produces.
Several factors explain the gap. Social desirability plays a role: people tend to round up. Inconsistent technique matters too. Pressing a ruler firmly into the pubic bone (the standard clinical method) gives a different reading than measuring loosely along the top. The amount of fat pad above the pubic bone also changes the visible length without changing the measured length. When comparing yourself to any average, the measurement technique matters as much as the number itself.
How to Measure Accurately
Clinical studies use a method called bone-pressed length, and it’s simple to replicate at home. You need a ruler or flexible tape measure and a full erection. Place the ruler along the top of the penis, press the end firmly against the pubic bone (pushing past any fat pad), and measure in a straight line to the tip. If your penis curves, a flexible tape measure along the top surface gives a more accurate reading than a rigid ruler.
For girth, wrap a flexible tape measure around the thickest part of the shaft at full erection. Most studies measure at mid-shaft. If you only have a string, mark it and then measure the string against a ruler.
What Counts as Unusually Small
Micropenis is a clinical diagnosis with a specific threshold: a stretched or erect length more than 2.5 standard deviations below the mean. In adults, that translates to roughly 3.66 inches (about 9.3 cm) erect or less. This is rare, affecting well under 1% of men. In newborns, the threshold is a stretched length under about 0.75 inches (1.9 cm).
If you fall within the normal range but still feel your size is inadequate, that perception is extremely common. Studies consistently find that most men who seek consultation about penis size fall well within normal measurements. The gap between perceived and actual averages is partly driven by unrealistic comparisons, whether from pornography or inflated self-report surveys.
Do Height or Shoe Size Predict Anything?
Barely. Height has the strongest correlation with erect length of any commonly cited body measurement, but the relationship is weak, with a correlation coefficient of about 0.30. In practical terms, that means height explains less than 10% of the variation in penis size. Shoe size and hand size show even weaker associations. A tall man is only slightly more likely to be above average, and plenty of shorter men measure well above the mean. There is no reliable way to estimate penis size from any external body measurement.
Does Size Change With Age?
Penile growth follows the timeline of puberty, typically reaching adult size by the late teens. After that, length remains stable for decades. Some gradual reduction can occur later in life, primarily due to reduced blood flow, lower testosterone levels, and increased fat deposition around the pubic area. The fat pad effect is reversible with weight loss, which can restore visible (though not actual bone-pressed) length. Maintaining cardiovascular health supports the quality of erections, which in turn affects functional size more than any fixed anatomical change.