Translate each percent grade to a letter grade. According to UScampus.com, most colleges and universities assess a grade of 90 to 100 percent as equal to an A, 80 to 89.9 percent equal to a B, 70 percent to 79.9 percent equal to a C, 60 percent to 69.9 percent equal to a D and below 60 percent equal to an F.
Convert each letter grade to a point value using the 4.0 system. An A has a 4-point value, B has a 3-point value, C has a 2-point value, D has a 1-point value and an F has a zero value.
Multiply the grade-point value by the number of credits received for the class. Then total the points. For example, an A for a three-credit class equals 12 (4x3=12) and a B for a two-credit class equals 6 (3x2=6). The total points equal 18 (12+6=18).
Add the credits earned together. As in the given example, the credits equal five (3+2=5).
Divide the sum of points by the sum of credits to calculate the GPA. In the example, the total point value is 18, divided by the five credits results in a 3.6 GPA.