Most US colleges work on a 4 point scale.
A=4, B=3, C=2, D=1, F=0.
Many schools no longer have D's.
Many schools have switch in recent years to a plus/minus system.
Type 1: A-/B+ = 3.5
Type 2: A- = 3.67, B+ = 3.33
Type 3: A- = 3.75, B+ = 3.25
Most schools do not have an A+, some do it's usually 4.25 or 4.33
Some schools have percentile scales (in addition to percentile rankings) others, still, have other GPA scales.
Harvard use to have a very odd 15 point scale which made it almost impossible to compare GPAs with other schools.
When I applied to law school, there was a Law School Admission Council which converted all the grades from school to school in to a uniform GPA. It's likely, that many graduate and professional schools weigh GPAs from different undergraduate schools according to rank or perceived quality.
I would cite regulation, but I know you will simply ignore it.
