Simple (non-weighted) averages and GPA
Every student should understand how their GPA is calculated. Often a student wants to calculate their GPA within their major, which they must do by hand. GPAs are calculated using a weighted-average, which is first illustrated by demonstrating a simple average (the one everyone knows).
Below are three courses a hypothetical student has taken, the hours they earn for each course, and their letter grade. Most GPAs are calculated on a 0 to 4 scale, where an F is given a score of 0 and an A is given a score of 4. This student made an A, B, and C, and if we took the simple average of the scores 4, 3, and 2, the GPA would be (4 + 3 + 2)/3 = 3.0. There are only three grades, and the simple average assigns each grade the same weight of one-third, as the average can be written as (1/3)(4) + (1/3)(3) + (1/3)(2) = 3.0.
[Equation 1] Simple average = (1/3)(4 + 3 + 2) = 3
Table 1—Hypothetical GPA Example
| Course | Hours of Credit | Grade |
| AGEC 1114 | 4 | A |
| AGEC 3333 | 3 | B |
| AGEC 4213 | 3 | C |
| Note: when calculating GPA an A, B, C, D, and F receive a numerical grade of 4, 3, 2, 1, and 0, respectively. | ||
The student's GPA is not really a 3.0 though. The reason is that AGEC 1114 course is a four-hour course, as the last number denotes the number of credit hours the course provides. Because AGEC 1114 provides the student with one more credit hour than the other two classes, it should count more. That is, when calculating GPA, AGEC 1114 should be given more weight.
Weighted averages and GPA
GPAs are calculated using a weighted-average, where each grade is "weighted" by the number of hours the course provides, divided by the total number of hours earned (here, 10). Equation 2 demonstrates this using the GPA example. Notice the (1/10) term comes from the fact that the student earned 10 credit hours from the three courses. When calculating GPA correctly using weighted-averages, the student is found to earn a 3.1, a bit higher than using the simple average, which is logical because she made an A in the course providing the most credit hours.
[Equation 2] Calculating GPA using a weighted average = (1/10)(4*4 + 3*3 + 3*2) = 3.1.
