Not necessarily, in my high school it was on a 4.0 scale, it all depends on where you go. To calculate you're GPA, you need to go to your register or go online to view Grades Completed or Transcript, it usually costs money (at least in college) to get official transcripts, but all you need is grades so they will calculate it for you. If you are trying to figure it out on your own, before grades are posted, you need to first consult the syllabus (all classes and GPA scales are different) and look at the percentages.