How to calculate APS?

Assuming that you mean the APS referring to college / high school subjects, it goes as follows:

There are a total of 8 levels on the APS, starting at 0, 2, 3, 4, 5, 6, 7, and 8

an 8 is a score of between 90% and 100%

7 is between 80 and 89%

6 is between 70 and 79%

5 is between 60 and 69%

4 is between 50 and 59%

vice versa ...

and a 0 is between 0 and 29%