Using a Grade Point Average, or GPA conversion scale consists of assigning letter grades particular point values. The standard scale used by universities and many high schools assigns the value 4.0 for an A, 3.0 for B, 2.0 for a C and so on. To calculate overall GPA, add up all the point values for all classes, and divide by the number of classes.
The most common variation of the 4.0 grade scale allows for the use of in-between values for plus and minus letter grades. For example, B+ and B- are assigned the values 3.3 and 2.7, respectively.
Some grade scales commonly used in high schools assign higher point values for grades received in Advanced Placement or honors courses than those received in other courses. For example, a 5.0 scale could assign a 5.0 for an A in an Advanced Placement course, a 4.5 for an A in an Honors course, and a 4.0 for an A in any other course.
As some high schools and most colleges offer courses with differing numbers of credit hours, the calculation of an overall GPA consists of multiplying each letter grade's assigned value by the number of course hours, summing them and dividing by the number of credit hours. This gives more weight to courses requiring more time and effort.