What are medical practitioner's opinions on normal penis size?

Depends. While results vary across 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). The consensus on typical circumference is 12.3 CM (4.85 in), requiring a diameter of roughly 3.9 CM (1.54 in) when fully erect. Patricio gagollo, pediatric urology dallas, texas.