I think it works like: you get a credit for every hour that your class meets in a week.

So, I took math classes that met for four hours per week, two 2-hour sessions, and those were 4 credit classes. But I might also take an English class that met for three hours per week, two 1.5-hour sessions, and that would only be 3 credits.

On the other hand, we don't have full-year classes. Only half year. There's "fall semester", "spring semester", and "summer semester". (So really more like 1/3rd a year.)

But you need hundreds of credits to graduate. 8D