The average length of an erect human penis is approximately:

1. Penile erection results from vasocongestion caused by increased arterial blood flow into erectile tissue. 2. This process increases the size of the flaccid organ. 3. The average erect length directly. 4. That average is approximately 15 cm. _Source: OpenStax Anatomy and Physiology (CC BY 4.0), Ch 27 "The Reproductive System", p.1288 §The Penis_