The 4.0 scale
On the standard unweighted scale, A is 4.0, A- is 3.7, B+ is 3.3, B is 3.0, B- is 2.7, C+ is 2.3, C is 2.0, C- is 1.7, D+ is 1.3, D is 1.0, and F is 0. Schools can use slightly different scales, so check your school's official scale for an official GPA.
How credits weight a course
Multiply each grade's points by that course's credits, add the results, and divide by total credits. A 3-credit course counts three times as much as a 1-credit course, even if the grades are the same.
An example
An A (4.0) in a 3-credit course and a B (3.0) in another 3-credit course gives (12 + 9) divided by 6, which is 3.50. Change the credits and the answer changes, even with the same grades.
What GPA does not say
A GPA is an average, not a full record. It does not show which courses were hard, which were easy, or how grades changed over time. Use it as a summary, not as a verdict.