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How Big Is the Average Penis? Science Finds Out (LiveScience)

"whether penis size truly matters to a man's sex partner is up for debate. Some research shows that women who experience vaginal orgasms do so more consistently with men of bigger girth."

How big is the average penis? (Science Magazine)
"According to the team's analysis, the average flaccid, pendulous penis is 9.16 cm (3.61 inches) in length; the average erect penis is 13.12 cm (5.16 inches) long. The corresponding girth measurements are 9.31 cm (3.66 inches) for a flaccid penis and 11.66 cm (4.59 inches) for an erect one."

Am I normal? A systematic review and construction of nomograms for flaccid and erect penis length and circumference in up to 15?521 men (BJU International)
"Stretched flaccid length appears to be an excellent estimate of erect penile length, which for some individuals presenting to clinical settings, may indicate that it may not be necessary to measure erect length as well as flaccid size. However, there was greater variability in the measures, which suggests less reliability."