These units are called credit hours. The principle behind the credit hour is that it represents the number of hours you spend in a classroom. In theory, for a one credit hour course, you should spend one hour per week in class throughout the semester. For a two credit hour course, you would spend two hours, and so on. In today s educational world, this is not always the case.
Homework also increases as credit hours increase.
You should always plan to spend three hours per week per credit hour completing homework. So, if you are taking 12 credits, plan to spend 12 hours per week in class, and 36 additional hours per week completing homework. Just as credit hours tell you how big a college course is, the class level tells you how advanced the course is. A 100 level course is designed for first year students, a 200 level course for second year students, a 300 level course for third year students and a 400 level course for fourth year students. This is a general principle, and not a requirement.