According to the 2011 Eligibility Count, Michigan ought to have 15 open scholarships for the Class of 2012. Nine redshirt seniors and six true seniors will be graduating after the 2011 season, assuming Kelvin Grady is a scholarship player. That also includes safety Mike Williams and defensive end Steve Watson, each of whom might depart before using up their eligibility (Williams due to concussions; Watson due to being buried on the depth chart).
That number will surely increase before February 2012 due to transfers, injuries, etc. The Class of 2011 was originally going to be around 14, and that number has ballooned to 20 (and counting). So the next class will likely be 20-ish as well.