In universities that operate under the semester hour system, one class credit is equal to one semester hour. To calculate how many semester hours a student is enrolled in, add up how many credits the student is taking.
At universities that operate under the semester hour system, most college classes are worth three credits. Sometimes, a class with a laboratory component is worth four credits, with three credits going towards the class and one credit going towards the laboratory. Generally, students are considered full time when they enroll in at least 12 credit hours. Therefore, full time students usually take at least 12 semester hours, or about four classes.