Assign grade points for every grade you have received in school. An "A" gives you 4 grade points, a "B" gives you 3 grade points, a "C" gives you 2 grade points, a "D" gives you 1 grade point and an "F" gives you none. Pluses or minuses vary according to the particular school. In some cases, a plus gives you an extra third of a point (a B+ gives you 3.33 points, for example) while a minus takes away one-third of a point (an A- gives you 3.67 points). In other schools, a plus gives you a half of a point. Consult the institution in question to determine the scoring system they use.
Add all of your grade points together. For example, if you attended four classes in a given semester, and earned an A (4.0), a B (3.0), a B+ (3.33) and a C+ (2.33), add them together to equal 12.66 grade points.
Divide your total number of points by the number of classes you attended. The result is your GPA. For example, divide the 12.66 grade points by 4 (the number of classes you took), and your GPA is 3.2.