How to calculate a grade percentage
Grade percentage = points earned ÷ points possible × 100. Quick examples (42/50 = 84%), how to combine several assignments, and how to round correctly.
Turning points into a percentage is the first step in every grade calculation. The method is the same for one quiz or a whole semester of points-based work.
One assignment
Divide what you earned by what was possible and multiply by 100. 17 out of 20 is 17 ÷ 20 = 0.85, so 85%. 42 out of 50 is 84%. 88 out of 120 is 73.33%.
Several assignments
Add all earned points, add all possible points, then divide. Do not average the individual percentages. Two quizzes at 18/20 (90%) and 42/50 (84%) are 60/70 = 85.71%, not 87%. The bigger assignment carries more weight because it has more points.
Quick reference
| Score | Percentage |
|---|---|
| 9 / 10 | 90% |
| 17 / 20 | 85% |
| 21 / 25 | 84% |
| 23 / 30 | 76.67% |
| 35 / 40 | 87.5% |
| 42 / 50 | 84% |
| 88 / 100 | 88% |
Full charts for every score: test score charts.
Rounding
Round only the number you display, never the one you compare against a letter boundary. 89.995% shows as 90.00% at two decimals but is still below 90. Instructors set their own rounding policy; some round to the nearest whole number, some never round. When it matters, ask.
From percentage to letter grade
Most US schools use a 10-point scale: 90–100 A, 80–89 B, 70–79 C, 60–69 D, below 60 F, often with plus and minus steps. Your syllabus is the authority. See the grading scale guide.