Theoretically, the maximum number you can receive is something like 256.
Here's two things you can do:
go to http://www.antennaweb.org/aw/Address.aspx and put in your address. It'll tell you what you can receive with each grade of antenna. It's not the best site, but it's the most newb friendly.
Option 2: go to tvfool.com . They are much better, but you've kinda got to geek out to use it.