Penis size

The most accurate measurement of the size of a human penis can be derived from several readings at different times since there is natural minor variability in size depending upon arousal level, time of day, room temperature, frequency of sexual activity, and reliability of measurement. When compared to other primates, including large examples such as the gorilla, the human penis is thickest, both in absolute terms and relative to the rest of the body. Measurements vary, with studies that rely on self-measurement reporting a significantly higher average than those with a health professional measuring. As of 2015, a systematic review of 15,521 men, and the best research to date on the topic, as the subjects were measured by health professionals, rather than self-measured, has concluded that the average length of an erect human penis is 13.12 cm (5.17 inches) long, while the average circumference of an erect human penis is 11.66 cm (4.59 inches). Flaccid penis length can sometimes be a poor predictor of erect length. Most human penis growth occurs between infancy and the age of five, and between about one year after the onset of puberty and, at latest, approximately 17 years of age. A statistically significant correlation between penis size and the size of other body parts has not been found in research. Some environmental factors in addition to genetics, such as the presence of endocrine disruptors, can affect penis growth. An adult penis with an erect length of less than 7 cm (2.8 in), but otherwise formed normally, is referred to in medicine as a micropenis. While results vary slightly across reputable studies, the consensus is that the mean human penis, when erect, is in the range 12.9–15 cm (5.1–5.9 in) in length. A 2015 systematic review published by Veale et al. of medical research on the topic over the previous 30 years published in BJU International showed similar results, giving mean flaccid, stretched non-erect, and erect lengths of 9.16 cm, 13.24 cm, and 13.12 cm respectively, and mean flaccid and erect circumferences of 9.31 cm and 11.66 cm respectively. Erect lengths in the included studies were measured by pushing the pre-pubic fat pad to the bone, and flaccid or erect girth (circumference) was measured at the base or mid-shaft of the penis. One study found the mean flaccid penis length to be 3.5 inches (8.9 cm) (measured by staff). A review of several studies found average flaccid length to be 9–10 cm (3.5–3.9 in). 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. 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 bicycle 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).