http://chronicle.com/blogs/profhacker/estimating-student-workload-for-your-courses/62515

“…Among the challenging decisions that instructors face in creating syllabi is the question of how much reading, writing, and other work to assign each week.

“The federal definition of course credit hours assumes a minimum of “two hours of out-of-class student work per week for a semester hour.” According to this metric, a student should assume at least six hours of out-of-class work per week for each 3-credit course.”

Note: “at least”

Also: http://www2.ed.gov/policy/highered/reg/hearulemaking/2009/credit.html