How GPA Is Actually Calculated (and Why Scales Differ)
GPA is a weighted average: each course's letter grade converts to a numeric grade point (A = 4.0, B = 3.0, and so on), that grade point is multiplied by the course's credit hours, and the total is divided by total credit hours across all courses. A 4-credit A affects GPA more than a 1-credit A, because credit hours act as the weight.
GPA looks like a simple average until you realize it's actually a weighted one, and that weighting — by credit hours, not just by grade — is exactly why a single heavy course can move the number more than people expect.
The letter-grade-to-points conversion
On the standard 4.0 scale, A equals 4.0 points, B equals 3.0, C equals 2.0, D equals 1.0, and F equals 0.0, with plus/minus variants typically adding or subtracting about 0.3 (an A- is commonly 3.7, a B+ commonly 3.3). This scale is widely used across US higher education, though the exact plus/minus values can vary slightly by institution.
Why credit hours act as a weight
GPA isn't a simple average of grade points — it's weighted by how many credit hours each course is worth. The calculation multiplies each course's grade points by its credit hours, sums all of those products, then divides by the total credit hours across every course.
This means a 4-credit course graded A contributes four times as much to the total as a 1-credit course graded A — which is exactly why a single demanding, high-credit course can shift an overall GPA more noticeably than a lighter elective, even with the same letter grade.
Why GPA scales aren't universal
The 4.0 scale is common but not the only one in use — some countries and institutions use a 5.0 scale (often for weighted honors or AP courses, adding an extra point), a percentage-based scale, or an entirely different grading system. Comparing GPAs across different scales requires converting to a common reference point first, since a 3.5 on one scale isn't automatically equivalent to a 3.5 on another.