Most surveys (medical and otherwise) put average somewhere between 5.5 and 6 long. (There's a high degree of variance between the surveys, which should tell you that they aren't accurate.)
If this concerns you,
www.thundersplace.com is an excellent forum for all forms of enlargement techniques. It's free. Although the moderator of it also loves donations, I'd say hold off until you get results and prove it to yourself.