Aug 23, - Let's compare with household objects. What's the average penis size? According to the new research in BJUI, the average flaccid penis is inches in length and inches in length when erect. Girth is inches when flaccid and inches when erect. Wondering what the average penis size is? Want to know how you compare to other guys? Enter your measurements and we'll work it all out for you and tell how Penis enlargement · Compare shape · Find your ideal condom · Measuring guide.