There is no authoritative data on how large the diameter of the penis is normal when erect, most people are at 2.2~2.8cm. The length of the penis varies from person to person. usually, in adult men, when not erect, the average length of the penis is 7~10cm, and when erect, the average length of the penis is 11~13cm, with a diameter of 2.2~2.8cm. if the length of the penis is less than 3cm in the relaxed state, it is known as a small penis. The normal penis length is independent of age and testicular volume, positively correlated with height and negatively correlated with weight. Penile diameter is independent of age and is positively correlated with height, weight and testicular volume. Medical attention is recommended if there is any obvious abnormality.