GPA stands for “Grade Point Average.” Grade point average is calculated this way: 4 points for an “A” grade, 3 points for a “B” grade, 2 points for a “C” grade, 1 point for a “D” grade, and zero points for an “F” grade. The highest possible theoretical GPA is a 4.0; every single person in the survey would need to give an "A" grade for that to happen.

By way of illustration: If, in a survey of 500 adults, responses divided as follows:

210 respondents gave an “A” grade (4),
160 gave a “B” grade (3),
 70 gave a “C” grade (2),
 10 gave a “D” grade (1),
 40 gave an “F” grade (0), and
 10 said they were not sure,

then the formula, to calculate the grade point average would be

((210 * 4) + (160 * 3) + (70 * 2) + (10 * 1) + (40 * 0))
-------------------------------------------------------- = 1470 / 490 = GPA of 3.00 = GPA of B.
                (210 + 160 + 70 + 10 + 40)