The average erect penis is about 5.1 to 5.5 inches (13 to 14 cm) long, depending on the study. That number comes from research where healthcare professionals did the measuring, not from self-reports. The average erect circumference (girth) is about 4.6 inches (11.7 cm). Most men fall surprisingly close to these figures, and sizes at the extremes are rare.
Average Length and Girth by the Numbers
Two large-scale reviews give the clearest picture. A 2015 analysis published in BJU International pooled data from 15,521 men measured by clinicians and found an average erect length of 5.16 inches (13.12 cm) and an average erect circumference of 4.59 inches (11.66 cm). A broader 2023 review in the World Journal of Men’s Health, covering 55,761 men across 75 studies from 1942 to 2021, placed the average erect length slightly higher at 5.49 inches (13.93 cm).
Flaccid measurements are less consistent because a non-erect penis changes size with temperature, arousal, and blood flow. Still, the BJU analysis found an average flaccid length of 3.61 inches (9.16 cm) and a flaccid circumference of 3.66 inches (9.31 cm). A separate study of over 15,000 men reported similar numbers: 3.6 inches flaccid length and 3.7 inches flaccid girth.
Where Most Men Actually Fall
The distribution is tighter than many people assume. Combining data from carefully controlled studies, about 68% of men measure between 4.6 and 6.0 inches (11.7 to 15.2 cm) when erect. Another 13.5% fall between 3.8 and 4.5 inches, and 13.5% between 6.1 and 6.8 inches. Only about 2.5% of men have an erect penis longer than 6.9 inches (17.5 cm), and only 2.5% measure under 3.7 inches (9.4 cm).
In other words, the vast majority of men are within about an inch of the average in either direction. Extremely large or extremely small penises exist, but they are statistical outliers.
How to Measure Accurately
Researchers use a consistent method so their data is comparable. European Association of Urology guidelines recommend measuring along the top (dorsal) side of the penis, from the pubic bone to the tip of the glans, while pressing a ruler or caliper gently into the fat pad above the base. This “bone-pressed” technique accounts for differences in body fat and gives the most reproducible number.
For girth, wrap a flexible measuring tape around the thickest part of the shaft. Measure when fully erect for the most meaningful comparison to published averages. If you’re comparing to the flaccid averages, measure at room temperature in a relaxed state.
Self-Reports vs. Measured Data
When men report their own size in surveys, the numbers consistently come in higher than when a clinician does the measuring. This matters because many widely cited statistics online are based on self-reported data. If you’ve seen claims that the average is six inches or more, those figures likely reflect this reporting bias. The clinician-measured average of roughly 5.1 to 5.5 inches is considered more reliable.
What Counts as a Medical Concern
A micropenis is a clinical diagnosis, not an informal label. It applies when a stretched penis length falls more than 2.5 standard deviations below the mean for a person’s age. In practical terms, the threshold for adults is about 2.95 inches (7.5 cm) stretched. For newborns, it’s less than 0.75 inches (1.9 cm). This is a rare condition, often identified at birth, and is typically linked to hormonal factors during fetal development.
If your measurements place you within or near the ranges described above, you are within normal variation. The clinical threshold exists far below what most men who worry about their size actually measure.
Does Size Change With Age?
The penis itself doesn’t shrink significantly as you get older. What does change is the tissue around it. Weight gain adds fat to the pubic area, which can make the visible portion of the shaft appear shorter. Reduced blood flow and lower testosterone levels in later decades can also affect how firm erections are, which may make the penis seem smaller during arousal even though the underlying structure hasn’t changed. The bone-pressed measurement technique effectively eliminates the visual effect of weight gain, which is one reason clinicians prefer it.