Human penis size is the measured length and width of the human penis. The most accurate measurement of the human penis comes from several measurements at different times, as there is natural variability in size due to arousal level, time of day, room temperature, frequency of sexual activity, and unreliability of the measurement methods. When compared to other primates, including large primates such as the gorilla, the genitalia of male humans are large, both in absolute terms and in relative size to the rest of the body. Results vary, with studies that rely on self-measurement reporting a significantly higher average than those with staff measuring, but a mean erect human penis is approximately 12.9–15.0 cm (5.1–5.9 in) in length. Flaccid penis length is a poor estimate of erect length. Most of human penis growth happens between infancy and the age of five, and in five years after the onset of puberty.
There is evidence both for and against a link between penis size and the size of other body parts. Some environmental factors in addition to genetic, such as the presence of endocrine disruptors, can affect penis growth. 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. Circumcised men are on average 8 millimeters shorter in terms of erect length compared to their intact counterparts.[1]
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Perceptions of penis size are culture-specific. In Ancient Greece and in Renaissance art, 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. Ancient Rome may have had a contrary view, and a larger penis size was preferred in medieval Arabic literature. Males may quite easily underestimate the size of their own penis relative to that of others, and many men who believe that their penis is of inadequate size have average-sized penises. The perception of having a large penis is often linked to higher self esteem.[2] For women, width rather than length is a more important factor of sexual stimulation.[3] Fear of shrinking of the penis in folklore have led to a type of mass hysteria called penis panic, though the penis legitimately can shrink in size due to scar tissue formation in the penis from a medical condition called Peyronie's disease.[4][5] Marketers of penis enlargement products exploit fears of inadequacy, but there is no consensus in the scientific community of any non-surgical technique that permanently increases either the thickness or length of the erect penis that already falls into the normal range.
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).[6][7][8] The consensus on typical circumference is 12.3 cm (4.85 in), requiring a diameter of roughly 3.9 cm (1.54 in) when fully erect.
Another reputable source claims that the relaxed (flaccid, non-tumescent) human penis has an average length of only 4 inches (≈10.2 cm) and a diameter of 1¼ inches (≈3.2 cm) (which would result in a circumference of roughly 3.9in/10.1 cm) while fully erect ones have an average length of 6 in (≈15.2 cm) and a diameter of 1½ inches (≈3.8 cm), resulting in an erect circumference of 4.71in/11.9 cm.[9]
The mean penis size is slightly greater than the median size. Studies have not found a relation between penis size and race.[10] Circumcised men are on average 8 millimeters shorter in terms of erect length compared to their intact counterparts.[1]
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.[11]
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."[12]
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],”[12] however, there is some evidence to suggest that testicle size is getting progressively smaller with younger cohorts.[13]
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.[8][14]
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.[14][15]
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).[6] A review of several studies found average flaccid length to be 9–10 cm.[12] Length of the flaccid penis does not necessarily correspond to length of the erect penis; some smaller flaccid penises grow much longer, while some larger flaccid penises grow comparatively less.[17][18]
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 phenomenon 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. An incorrect saddle may ultimately cause erectile dysfunction (see crotch pressure for more information).
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.[12]
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.[19] The condition affects 0.6% of men.[18] 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.[20]
It has been suggested that differences in penis size between individuals are caused not only by genetics, but also by environmental factors such as culture, diet, chemical/pollution exposure,[21][22][23][24] 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[25][26]) sources have been linked to various degrees of endocrine disruption. Both PCBs and the plasticizer DEHP have been associated with smaller penis size.[27][28] 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.[29] Approximately 25% of US women have phthalate levels similar to those in the study.[29] A 2007 study by University of Ankara, Faculty of Medicine has found that penile size may decrease as a result of some hormonal therapy combined with external beam radiation therapy.[30] In addition, some estrogen based fertility drugs like diethylstilbestrol (DES) have been linked to genital abnormalities and/or a smaller than normal penis (microphallus). [31]
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, usually being found on "fertility gods, half-animal critters such as satyrs, ugly old men, and barbarians."[33]
CBC radio has suggested, based on several sources, that ancient Romans had a viewpoint contrary to that of the Greeks.[32] 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".[34]
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.19 Yet she turned to even greater prostitution, remembering her youth when she was a prostitute in Egypt.20 She 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 [35]
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.[36] A survey by sexologists showed that many men who believed that their penis was of inadequate size had average-sized penises.[37] 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.[38] The perception of having a large penis is linked to higher self esteem.[2]
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.[39] One study analysing the self-reported Kinsey data set found that homosexual men had statistically larger penises than their heterosexual counterparts.[40] One potential explanation given is a difference in the exposure to androgen hormones in the developing embryo. Evidence points towards men of both orientations being equally likely to exaggerate the size of their penises.[41]
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. The penis can significantly shrink due to scar tissue formation from a condition called Peyronie's disease which affects up to 10% of men.[42] Products such as penis pumps, pills, and other dubious means of penis enlargement are some of the most marketed products in email spam. At present there is no consensus in the scientific community of any non-surgical technique that permanently increases either the thickness or length of the erect penis that already falls into the normal range (4.5" to 7").[43]
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.[44] Another investigation failed to find any evidence for a link between shoe size and stretched penis size.[45][46]
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)[47] 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).[48]
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.[3]
Similar results were found in a cover story published in Psychology Today,[49][50] 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".[51]
The term size queen is slang for a person who prefers their sexual partner(s) to have a larger-than-average penis.[52][53]
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.[54] (see Implications of differences in penis length and morphology for hypothesized advantages involving group sex which may have led to the evolution of a larger penis size in humans, and factors which may account for differences in average penis size within the human species).
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.[55]