Men believe average erect penis exceeds 6 inches. Self-reported studies yield 6.2 inches due to biases. Researcher-measured erect penises average 5.36 inches across 1629 men. Stretched flaccid penises average 5.11 inches across 13719 men. Volunteer bias inflates measurements in many studies. Social desirability makes men over-report penis length. Gay men self-report even larger sizes than straight men. Only 12-17% of men exceed 6.3 inches erect. Korean men average 4.68 inches erect. Most men seeking lengthening surgery have normal sizes. Women estimate average closer to reality at 5.29 inches. Penis length correlates with height and index finger length. No evidence of racial differences in penis size. No evidence of sexual orientation differences in penis size. 45-68% of men wish for larger penises. Counseling reduces size anxieties better than risky surgery. Self-reports unreliable even with partner measurement. Pornography and media fuel size myths. Women largely satisfied with partner penis sizes. surgeries on normal penises carry high risks.