It appears that there are about 3 hours of grading per week for each 3 hours spent in class.
My university counts our time for these courses like this: 3 hours in class, 3 in consultation with students, 3 hours of preparation, and 3 hours of grading. I suppose it is accurate enough except for the preparation time, which does grow quite a lot if you have any reading to do.
What do you find? I have colleagues who say that only graduate courses have reading it takes more than an hour to do. I find this odd, but as a revelation it explains a great deal.