The formula
GPA = Σ(grade points × credits) ÷ Σ(credits that count in GPA).
Every course contributes quality points equal to its grade points multiplied by its credit hours. The GPA is the total quality points divided by total counted credits.
A worked example
An A- (3.7 points) in a 3-credit course gives 11.1 quality points. A B+ (3.3) in a 4-credit course gives 13.2. Together: 24.3 points ÷ 7 credits = 3.47 GPA.
Grades like P, W and audit are typically excluded from both the numerator and the denominator.
Why scales differ
Schools assign different point values to the same letter — an A- is 3.75 at UCF, 3.67 at the University of Florida, and 3.7 at UC Berkeley. Always check the scale your school publishes.