GPA stands for "Grade Point Average". It's a standard way of measuring achievements in high school or college. In other words, it's an average number that shows what you have scored in your classes throughout the term, semester, and year.
Mostly, the grade point average is calculated on a 4.0 scale. So, it may count in the range from 0.0 to 4.0.
0.0 defines the lowest score, and 4.0 defines the highest score. In addition, this type of GPA is known as an "Unweighted GPA".
But some academics consider Advanced Placement(AP) or Honors classes for extra points. So, they consider 5.0 as the highest score and it's known as a "Weighted GPA".
Also, check out the standard deviation calculator. It will surely be helpful in your study.