Here's a great (and free) tool to assess your route options. http://www.mapmyride.com/
One of the options (toolbar on the right) once you begin mapping is the "show elevation" button, which shows elevation profile and grade. The grade is averaged, so the longer your route the more "distilled" the actual grade - so if you have any short, steep efforts, you can only map the segment in the vicinity of the hill to get the grade info.

Anyway, I'd say up to 3% average grade can be handled with a 3-speed or a singlespeed mountain/cyclocross bike. Anything more is adding functionality for riding with loads and/or in very windy conditions.