Units may not be the best way to predict your workload for a quarter. Rather, focus on the number of assignments—how many exams, essays, problem sets, reading responses will you need to do this quarter?
One tool you can use to evaluate your workload is a sheet that lets you see all your major deadlines at once. You can use the Quarter-At-A-Glance planner provided by VPTL's Academic Skills Coaches, or a spreadsheet, or type a list with deadlines week-by-week, or something like Google Calendar. Whatever system works for you is fine—but it’s important that you can look at the whole quarter on a single page (or screen), and see the full commitment you are making that quarter.
You should definitely enter the due dates for all major exams, essays, and final exams or final projects. Some students will also enter problem sets or smaller assignments in the overall list of deadlines—you might color-code these so that major deadlines still stand out. In addition, if you have significant commitments for extracurricular activities, you probably want to include those.
This tool can be used early in the quarter, as you decide on the best combination of classes for you to take. What appears to be a nicely balanced set of courses might prove unsustainable because all of your midterms fall on the same two days. Knowing what shape your quarter will take (in terms of exams, projects, finals, and so forth) can help you make good choices and might help you decide between two equally attractive courses.
If conflicting deadlines were unavoidable, then you’ll need careful planning and advance notice to make it work—if you have two essays due the week after next, then can you move some of that work to next week? If all your exams are very close together, then creating weekly review sheets as you go through the quarter will help you study more efficiently. And so forth.