How Percentiles Map to Curved Letter Grades
The classic 10–20–40–20–10 bell-curve distribution
F
10%
D
20%
C
40%
B
20%
A
10%
0
10
30
50
70
90
100
Percentile rank →
z=−1.28
z=−0.52
z=+0.52
z=+1.28