The number of credits does not necessarily correlate to undergrad, but I have heard it would be like 24-30 credits per semester.
Here is Ohio State's Class schedule and exam schedule (click the links in the middle of the page). All of the schools that I have interviewed and research have all reported very similar "9-5" schedules. So expect class early in the morning (going to be 7:30 for me at OSU...) and getting out in the late afternoon followed by studying in the evening. Its going to be busy and a lot more work than most are used to no matter where you go.
But then again, I haven't walked the walk yet.