Apr 17, Research says the average length is inches for a flaccid penis and inches for We'll explain how to measure your penis, whether size matters for sexual Put your hard knowledge to the test against these 12 facts. Mar 7, Your penis spends most of its time in a flaccid state. But did you know that the size of a flaccid penis has no relationship to the size of an erect one? Or that most Put your hard knowledge to the test against these 12 facts. The average size of an adult erect (hard) penis is 5 to 7 inches long. The size of your penis when it's flaccid (soft) doesn't have much to do with its size when it's.