Make a list of each grade you received in a class and the total number of units for that class. Making a list will help you make sure you include every class and grade in your GPA calculation.
Convert the letter grades into numerical scores. An "A" or "A+" is worth 4 points, and each descending level of grade is worth 1/3 point less rounded to two decimal points. An "A-," for example, is worth 3.67 points, a "B+" is worth 3.33 points and a "B" is worth 3 points. An "F" is worth 0 points.
Multiply the numerical score for each grade by the number of units that class was worth. If you got an "A-" in a 4-unit class, for example, you would multiply 3.67 times 4 for a total of 14.68. If you also got a "B-" in a 3-unit class, you would multiply 2.67 times 3 for a total of 8.01.
Add together the numbers you calculated. In our example, you would add together 14.68 and 8.01 for a total of 22.69.
Divide the number you calculated by the total number of units you took and included in your prior calculations. In our example, you took a 4-unit class and a 3-unit class for a total of 7 units, so you would divide 22.69 by 7 for a total of 3.24. This number is your GPA.