How many PhD programs should you apply to? That depends on a few things. First, what is your goal? Are you applying for PhD programs in order to get a job as a professor, or are you interested in having more options for non-academic careers? Or are you just interested in learning more about your field, and getting a PhD is the best way to do that? 

 The answer also depends on how hard it is for somebody with your background to get into PhD programs. Some fields have very few openings and receive hundreds of applications; other fields have lots of openings and don’t receive many applications. If you are in an easy field to get into, then you probably want to aim to apply to at least 2 or 3 schools. In a harder field, 10 schools might be appropriate.