The average normal penis length is 8.8 cm when flaccid and 12.9 cm when erect. Usually not too much difference from the average is normal. The normal male penis does not vary too much from the average size, and there are also differences in penis size between the flaccid case and the erect length. In both cases, there is an average penis length. Patients can compare them based on the average size. Some studies have shown that the size of a male’s erect penis is not related to the size of his flaccid penis. This means that men with different penis lengths when flaccid may have similar sized erect penises. There is also no relationship between a man’s age and penis size. Usually, it is considered normal as long as the difference in the average is not too big. There are sometimes diseases that can cause length differences, but most of these can be detected. Patients who notice a change in their length need to seek professional medical help. The length of the penis is mainly measured in the erect and weak state respectively. The length is 8.8 cm when flaccid and 12.90 cm when erect, which is different in both cases.