Human penis size is the measured length and width of the human penis.
Measuring the penis
To get the most accurate measurements for an individual's penis size, it has been recommended that several measurements be taken at different times, preferably with different erections on different days. The measurements are then to be averaged together. This is to account for what may be natural variability in size due to factors such as arousal level, time of day, room temperature, frequency of sexual activity, and unreliability of the measurement methods.
The length can be measured with the subject standing and the penis held parallel to the floor. The penis is measured along the top, from the base to the tip. Results are inaccurate if the measurement is taken along the underside of the penis, or if the subject is seated or prone.
Penis girth is the measurement of the circumference of the completely erect penis. It is variously quoted as an average of three measurements: just below the glans penis, in the middle of the shaft, and at the base.
A penis must be completely erect in order to obtain an accurate measurement. This may be difficult to achieve in a clinical setting. At least one Brazilian doctor resorted to injecting penises with drugs to induce erection, which gave more consistent results. Some clinicians measure the penis by stretching the flaccid penis as far as comfortably possible.
Studies on penis size
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].”
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.
- 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.
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.
Variance in penis size
An adult penis with an erect length of less than 7 cm or just over 2 inches but otherwise formed normally is referred to in a medical context as having the micropenis condition. The condition affects 0.6% men. Some of the identifiable causes are deficiency of pituitary growth hormone and/or gonadotropins, mild degrees of androgen insensitivity, a variety of genetic syndromes, and variations in certain Homeobox genes. Some types of micropenis can be addressed with growth hormone or testosterone treatment in early childhood. Operations are also available to increase penis size in cases of micropenis in adults.
Environmental influence on penis size
It has been suggested that penis size differences between individuals is caused not only by genetics, but also by environmental factors such as culture, diet, chemical/pollution exposure, etc. Endocrine disruptor resulting from chemical exposure has been linked to genital deformation in both sexes (among many other problems). Chemicals from both synthetic (e.g. pesticides, anti-bacterial Triclosan, plasticizers for plastics, etc...) and natural (e.g. chemicals found in tea tree oil and lavender oil) sources have been linked to various degrees of endocrine disruption. Both Polychlorinated biphenylPCBs and the plasticizer DEHP have been associated with smaller penis size. DEHP metabolites measured from the blood of pregnant women have been significantly associated with the decreased penis width, shorter anogenital distance, and the incomplete descent of testicles of their newborn sons, replicating effects identified in animals. Approximately 25% of US women have phthalate levels similar to those in the study.
Perceptions of penis size
Fresco of Priapus
. Depicted weighing his large erect penis against a bag of gold. Ancient Romans admired the large penis of Priapus.
In ancient Greek art, it is common to see smaller male genitalia than one would expect for the size of the man. Renaissance art also followed this aesthetic; note Michelangelo's David. According to Kenneth Dover's landmark study "Greek Homosexuality", Greek art had extreme interest in the genitals, but was not obsessed with size.
The weekly Q&A column "The Straight Dope" deduces, based on pornographic Greek art work and Dover's aforementioned study, that in ancient Greece an uncircumcised and small penis was culturally seen as desirable in a man, whereas a bigger or circumcised penis was viewed as comical or grotesque (at least in the high-brow view), usually being found on "fertility gods, half-animal critters such as satyrs, ugly old men, and barbarians."
CBC radio has suggested, based on several sources, that ancient Romans had a viewpoint contrary to that of the Greeks. This was also the case in medieval Arabic literature, where a longer penis was preferred, as described in an Arabian Nights tale called "Ali with the Large Member". As a witty satire of this fantasy, the 9th century Afro-Arab author Al-Jahiz wrote: "If the length of the penis were a sign of honor, then the mule would belong to the (honorable tribe of) Quraysh".
Penis size is also alluded to in the Bible:
“In the same way, I became disgusted with Oholibah and rejected her, just as I had rejected her sister, because she flaunted herself before them and gave herself to satisfy their lusts. 19Yet she turned to even greater prostitution, remembering her youth when she was a prostitute in Egypt. 20She lusted after lovers with genitals as large as a donkey’s and emissions like those of a horse. Ezekiel 23:18–20, New Living Translation 
Males may quite easily underestimate the size of their own penis relative to that of others, because of the foreshortening obtained from looking down, or because of the accumulation of fat at the base of the penis. A survey by sexologists showed that many men who believed that their penis was of inadequate size had average-sized penises. Another study found sex education of standard penile measurements to be helpful and relieving for patients concerned about small penis size, most of whom had incorrect beliefs of what is considered medically normal. The perception of having a large penis is linked to higher self esteem in general, but also among gay men specifically.
Among gay men
A study undertaken at Utrecht University found that the majority of homosexual men in the study regarded a large penis as ideal, and having one was linked to self esteem. One study analysing the self-reported Kinsey data set found that homosexual men had statistically larger penises than their heterosexual counterparts. One potential explanation given is a difference in the exposure to androgen hormones in the developing embryo. Evidence points towards men of each of these two orientations being equally likely to exaggerate the size of their penis.
Anxiety about penis size
Widespread private concerns related to penis size have led to a number of folklore sayings and popular culture reflections related to penis size. Penis panic is a form of mass hysteria involving the believed removal or shrinking of the penis, known as genital retraction syndrome. Products such as penis pumps, pills, and other dubious means of penis enlargement are some of the most marketed products in email spam.
Penis size and size of other body parts
There is evidence both for and against a link between penis size and the size of other body parts. One study found a weak correlation between the size of the stretched penis and foot size and height. Another investigation failed to find any evidence for a link between shoe size and stretched penis size.
A potential explanation for a link is that the development of the penis in an embryo is controlled by some of the same Hox genes (in particular HOXA13 and HOXD13) as those that control the development of the limbs. Mutations of some Hox genes that control the growth of limbs cause malformed genitalia (hand–foot–genital syndrome).
Studies of size preferences among sexual partners
A study published in BMC Women's Health, surveyed women's preferences concerning penis size and concluded that width rather than length is a more important factor of sexual stimulation.
Similar results were found in a cover story published in Psychology Today, which surveyed 1,500 readers (about 2/3 women) about male body image. Many of the women were not particularly concerned with penis size and over 71% thought men overemphasized the importance of penis size and shape. Generally, the women polled cared more about width than men thought, and less about length. "...the number one reason women preferred a thicker penis was that it was more satisfying during intercourse."
Another study, conducted at Groningen University Hospital, asked 375 sexually active women (who had recently given birth) the importance of penis size and concluded: "Although clearly in the minority, a nevertheless considerable percentage of the women respondents attached substantial importance to the size of the male sexual organ".
The term size queen is slang for a person who prefers their sexual partner(s) to have a larger-than-average penis.
Comparison to other primates
When compared to other primates, including large primates such as the gorilla, the genitalia of male humans are large. The human penis is both longer and thicker than that of any other primate, both in absolute terms and in relative size to the rest of the body.
Penis size and condom use
One Australian study of 184 men looked at penis length and circumference in relationship to condom breakage or slippage. 3,658 condoms were used. The study found that condoms, when used correctly, had a breakage rate of 1.34% and, of slippage, 2.05%, with a total failure rate of 3.39%. Penis length did not influence slippage, but penis circumference and broken condoms were strongly correlated, with larger sizes increasing the rate of breakage.
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- EurekAlert! summary
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