Two students each get one A and one C this term. Their GPAs can still come out meaningfully different — because GPA isn't a simple average of grades, it's an average weighted by how many credit hours each course was worth.
The formula
GPA = sum(grade points × credit hours for each course) / sum(credit hours)
Every course contributes to both the top and bottom of that fraction in proportion to its own credit hours — a bigger course pulls your GPA further in whichever direction its grade points sit, simply because it's weighted more heavily in both sums.
A worked example
Student A: an A (4.0 grade points) in a 4-credit course, and a C (2.0 grade points) in a 1-credit course.
(4.0 × 4 + 2.0 × 1) / (4 + 1) = (16 + 2) / 5 = 3.6
Student B: the same two letter grades, but reversed — an A in the 1-credit course, a C in the 4-credit course.
(4.0 × 1 + 2.0 × 4) / (1 + 4) = (4 + 8) / 5 = 2.4
Identical letter grades — one A, one C, for both students — but a 1.2 point difference in the resulting GPA, purely because of which course each grade landed in. Student A's A landed in the bigger course and pulled the average up; Student B's A landed in the smaller course and couldn't offset the C in the bigger one nearly as much.
The practical takeaway
A struggling grade in a high-credit course (a full lab science, a core major requirement) has a bigger effect on your overall GPA than the same struggling grade in a 1-credit seminar or elective — and conversely, a strong grade in a big course does more for your GPA than a strong grade in a small one. Worth keeping in mind when deciding where to invest extra effort during a demanding term, if the goal is specifically to protect or improve GPA.
Using the tool
Our GPA/CGPA Calculator applies this exact credit-weighted formula — enter each subject's grade points and credit hours, and it handles the weighting automatically, including showing how many subjects and total credits were counted.
Try it here: GPA/CGPA Calculator.