While results vary across studies, the consensus is that the mean human penis is approximately 12.9–15 cm (5.1–5.9 in) in length with a 95% confidence interval of (10.7 cm, 19.1 cm) (or, equivalently, 4.23 in, 7.53 in). The typical girth or circumference is approximately 12.3 cm (4.85 in) when fully erect. Yet, one reputable source claims that the relaxed human penis has an average length of only 4 inches (≈10.2 cm) and diameter of 1¼ inches (≈3.2 cm) while fully erect it has an average length of 6 inches (≈15.2 cm) and diameter of 1½ inches (≈3.8 cm).The mean penis size is slightly greater than the median size. Studies have not found a relation between penis size and race.
Size at birth
Frequency graph of LifeStyles length data.
Percentile plot of LifeStyles length data.
Frequency plot of LifeStyles circumference data.
Percentile plot of LifeStyles circumference data.
The average stretched penile length at birth is about 4 cm (1.6 in), and 90% of newborn boys will be between 2.4 and 5.5 cm (0.9 and 2.2 in). Limited growth of the penis occurs between birth and 5 years of age, but very little occurs between 5 years and the onset of puberty. The average size at the beginning of puberty is 6 cm (2.4 in) with adult size reached about 5 years later. W.A. Schonfeld published a penis growth curve in 1943.
Size with aging
Authors of a paper reviewing research on area of penis sizes conclude that "flaccid penile length is just under 4 cm at birth and changes very little until puberty, when there is marked growth."
Age is not believed to negatively correlate with penis size. “Individual research studies have… suggested that penis size is smaller in studies focusing on older men, but Wylie and Eardley found no overall differences when they collated the results of various studies [over a 60 year period].”
Erect length
Several scientific studies have been performed on the erect length of the adult penis. Studies which have relied on self-measurement, including those from Internet surveys, consistently reported a higher average length than those which used medical or scientific methods to obtain measurements.
The following staff-measured studies are each composed of different subgroups of the human population (i.e. specific age range and/or race; selection of those with sexual medical concerns or self-selection) which could cause a sample bias.
- A study published in the September 1996 Journal of Urology concluded that average erect length was 12.9 cm (5.08 in) (measured by staff). The purpose of the study was to “provide guidelines of penile length and circumference to assist in counseling patients considering penile augmentation.” Erection was pharmacologically induced in 80 physically normal American men (varying ethnicity, average age 54). It was concluded: “Neither patient age nor size of the flaccid penis accurately predicted erectile length.”
- A study published in the December 2000 International Journal of Impotence Research found that average erect penis length in 50 Jewish Caucasian males was 13.6 cm (5.35 in) (measured by staff). Quote: "The aim of this prospective study was to identify clinical and engineering parameters of the flaccid penis for prediction of penile size during erection." Erection was pharmacologically induced in 50 Jewish Caucasian patients who had been evaluated for erectile dysfunction (average age 47±14y). Patients with penis abnormalities or whose ED could be attributed to more than one psychological origin were omitted from the study.
- A study conducted by LifeStyles Condoms found an average of 14.9 cm (5.9 in) with a standard deviation of 2.1 cm (0.8 in) (measured by staff). The purpose of this study was to ensure properly sized condoms were available.
- A review published in 2007 issue of BJU International, have shown that average erect penis length is 14–16 cm (5.5–6.3 in) and its girth is 12–13 cm (4.7–5.1 in). This paper compares results of twelve studies conducted on different populations in several countries.
- An Italian study of about 3,300 Italian men concluded that stretched length was measured on average to about 5 inches (13 cm). In addition, a correlation between weight and height and penis length was also found. However this was done only on 500 men with a small correlation value.
Erect circumference
- The Cancún LifeStyle study, in which the circumference of the shaft was measured at three points (base, mid-shaft, and just below the head) and then averaged, found an average of 12.63 cm (4.972 inches) with a standard deviation of 1.3 cm (0.5 in).
Similar results exist regarding studies of the circumference of the adult fully erect penis, with the measurement taken mid-shaft. As with length, studies that relied on self-measurement consistently reported a significantly higher average than those with staff measuring.
Flaccid length
One study found the mean flaccid penis length to be 3.5 inches (8.9 cm) (measured by staff). A review of several studies have shown average flaccid length to be 9–10 cm. Length of the flaccid penis does not necessarily correspond to length of the erect penis; some smaller flaccid penises can grow much larger, and some larger flaccid penises cannot grow much larger.
The penis and scrotum can contract involuntarily in reaction to cold temperatures or nervousness, referred to by the slang term "shrinkage", due to action by the cremaster muscle. The same issue affects cyclist and exercise bike users, with prolonged pressure on the perineum from the saddle, and the straining of the exercise causing the penis and scrotum to contract involuntarily which is sometimes referred to as "gym balls" or "saddle balls". An incorrect saddle may ultimately cause erectile dysfunction (see crotch pressure for more information).
Penises that are short when flaccid but substantially larger when erect are colloquially known as "growers", while those with greater flaccid lengths that increase little when erect are known as "showers".
Flaccid penis length is a poor estimate of erect length; a better estimate is stretched length, that is 12–13 cm, as shown in review by Wylie and Erdley.
See also natural penis enlargement methods
