There is no magic number. Some say 6-8 colleges, others say up to 12. At IvyWay we recommend minimum 6 colleges, maximum 10. But if you need financial aid, applying to 12 is adequate because that way you can compare financial aid awards.
The important thing here is for you to analysis yourself and see if the college fits with your college needs. Do not just apply because it's free, your father or your mother went there or, worse, your boyfriend or girfriend are thinking about applying. Apply because you truly like what you see and believe that you will be successful and happy there.
Please read this article on how many schools you should apply to and the parameters that a student should consider when doing so: