Look up your alphabetic to numeric grade converter in your school's course catalog. This tells you how many points a letter grade is worth. Schools usually use a 4 for an A, 3 for a B, 2 for a C, 1 for a D and 0 for an F. However; how schools treat decimal places for pluses and minuses varies.
Multiply the numeric grade by the number of credit hours the course is worth. This is your quality points for the course. For example; if you have an A in a three-credit course and an A is worth 4 points, then 4 x 3 = 12 quality points.
Add together all your quality points for your classes to calculate your total quality points while in college.
Add together all your credits to find your total credits you took while in college.
Divide your total quality points from Step 3 by your total credits taken from Step 4 to calculate your GPA.