or length of the erect penis that already falls into the normal range. While results vary slightly across reputable 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). [5]