another older thread on weighted gpa calculation. keep in mind a lot of colleges use only the core courses for GPA calculation. even the unweighted gpa can be different from the high school calculation.
USC uses the SC UGP system. All of the high school classes here in SC will give you a number grade instead of an A-F. So your 6 classes can look something like 84, 88, 89, 92, 94, 95 (3 As, and 3Bs). An 84 will read as 3.4 for a core class, 3.9 for honors, and 4.4 for AP/IB/dual enrollment (although I don’t know if USC counts out of state honors in the same light).
Using that example, 3 As and 3 Bs (as long as each course is worth 1 unit each) would give you the usual GPA of 3.5. But with the SC UGP system, those grades would give you a GPA of 4.03. South Carolina has this system because of the cut-off in state scholarships.