To calculate an average grade, first add up all the individual grades, then divide by the total number of grades. Letter grades or percentage grades can be converted to the 4.0 scale to find the grade point average, or GPA.
For example, any score from 93 to 100 percent is an A or A+, and it is worth four points on the 4.0 scale. An A- is 90 to 92 and worth 3.7 points. Calculate each grade into a numeric value, either as a percentage or on the 4.0 scale. Then, add all these numbers together. Finally, divide by the total number of grades. This results in the arithmetic mean, the number most commonly thought of as the average. However, the word "average" can be used to refer to the median, the mode or another type of calculation. Adjust depending on which is desired.