A score of 64 out of 100 corresponds with a letter grade of D, based on most common grading scales. This grade is also equal to 1 grade point on the common grade-point-average or GPA scale.
According to most American educational standards, letter grades are assigned to each number grade based on a scale of 1 to 100. The letter grades are as follows:
- A = 90 to 100
- B = 80 to 90
- C = 70 to 80
- D = 60 to 70
- F = 0 to 60
Some schools also use + or - signs when assigning a grade. For instance, a 72 out of 100 would be equivalent to a C-, while a 78 out of 100 would be a C+.