GPA Calculator. Use this GPA calculator to calculate your GPA score. You can input up to 150 courses in this calculator. New row will be added automatically by clicking the last row.The score fields can take number as well as alphabetical scores as listed in the equivalent scores list. The credit fields need to be numerical.t is the average of the grades on all courses with course credit considered. The grading systems are very different in different countries or even schools. This calculator can take any numerical grade systems as well as the classical five-point system (A, B, C, D, or F).