The answers to the following questions are based on original research data collected by Dr. Alfred Kinsey and his research team.
Q. What is the range of erect penis length for most men?
A. 5–6.5 inches*
Q. What is the average circumference?
A. 4–5 inches*
Men were asked: "How long is your penis, measuring on the top side from your belly out to the tip?" They were each given a pre-stamped card to take home, and instructed to mark the length on the card when flaccid and when erect. Approximately 2,500 men participated.
During interviews with over 4,000 men, the interviewer asked each subject to estimate his penis size. The interviewer would hold out a ruler (the numerals were not visible to the subject) and move his finger along it.
There was a slight underestimation of penis size compared with actual measurements.
(Gebhard & Johnson 1979, p. 116.)
There is a much wider range of size in men's penises when flaccid, with the average ranging from 1 to 4 inches. In general, smaller, flaccid penises lengthen at erection by a greater percentage than larger, flaccid penises, with most men reaching an average size of 5 to 7 inches. This means the flaccid size of a penis is not a good predictor of erect size. The vast majority of men measure within the average genital size range and have a penis size that is more than adequate for sexual functioning.
This term is used by researchers to refer to penises less than 2.8 inches (7 centimeters) in length when stretched. This condition is thought to affect only 0.6% of men (or six in 1,000 men) and caused by inadequate testosterone at a late stage of fetal development.
There is no non-surgical technique to make the penis bigger. Penis pumps may help create a stronger erection, but they will not create a larger penis. Because the penis is composed largely of spongy erectile tissue and not of muscle, it cannot be strengthened or "built up." Surgery may cause scar tissue to grow that can cause a painful or even a shortened erection.
Below is a selected bibliography of research resources related to penis size compiled in response to frequent questions received by the Institute.
For a review of penis size studies, see Wylie, K.and Eardley, I. Penile Size and the 'Small Penis Syndrome.' BJU International, 99(6) 1449-1455