Gather all applicable grades for the desired type of GPA calculation: term (or semester), school year, or cumulative (entire duration while at an institution)
Assign a numerical value to each letter grade. Assign 4 to an A, 3 to a B, 2 to a C, 1 to a D and 0 for any failing grades. Do not calculate pass-or-fail basis classes. Pluses and minuses do not change the number assigned to each grade.
Add the total of those numerical values. Double-check your answers, writing down the results of each separate calculation to be weighed against potential discrepancies.
Divide that number by the total number of classes taken.
Record this number, which should be between 0 and 4. This is your unweighted GPA. If the number is outside of that range, there is an error in your calculation and you should begin the process again.