Figure your average by adding the total percentages of your assignments, assuming they are all weighted the same. Divide that total by the number of assignments. For example, for five papers, each worth one-fifth of your total grade, you got 85, 93, 72, 99 and 90 percent. Add those numbers to get 439. Divide 439 by the number of assignments, in this case, five. You get 87.8 percent.
Match your percentage to the grade guidelines for your class. Often, 90-100 percent equals an A, 80-89 percent equals a B, 70-79 percent equals a C, 60-69 percent equals a D and anything below 60 equals an F.
For points-based classes, add to get your total number of earned points. Divide that total by the total points possible. For example, if you earned 94 points and there are 120 possible points in your class, divide 94 by 120 to get 78 percent. Look up your percentage on the course syllabus to determine what your letter grade is in the class.