How to Calculate Grading
What the student got right, divided by what was possible, times 100 gives the percent, and the letter comes from the exact percent.
Three ways to work out a grade
- Count wrong: take the total question count, subtract the wrong answers, divide that result by the question count, then multiply by 100. When there are 20 questions and 3 are wrong, 17 ÷ 20 × 100 = 85%.
- By points: work out points earned ÷ points possible, then multiply by 100. With 42 points earned out of 50 available, 42 ÷ 50 × 100 = 84%.
- Partial credit: a half-right answer counts as 0.5, and you can use either method. For 8 questions where 1.5 are wrong, 6.5 ÷ 8 × 100 = 81.25%.
Rounding the percent
Whole numbers stay the same, so 85% appears as 85%. Every other percent takes one decimal place, rounded half up: 81.25% turns into 81.3%, and 2 out of 3 turns into 66.7%.
Reading the letter grade
Always use the exact percent for the letter, not the rounded one. The plus-minus scale puts A− at 90 and up, so 89.5% gets a B+. If a school rounds up, it can set that cut-off at 89.5.
Find out the number of questions a student is able to miss
Each letter grade starts from the number of questions: multiply it by the gap between 100 and the cut-off, divide by 100, then round down. The A− at 90 on a 25-question test leaves room for 2 misses (92%), because 25 × 10 ÷ 100 = 2.5. After that, the grader checks the count against the exact percent.
Examples worked through
| Questions | Wrong | Scale | Percent | Grade |
|---|---|---|---|---|
| 20 | 3 | Plus-minus | 85% | B |
| 25 | 4 | Plus-minus | 84% | B |
| 40 | 7 | Plus-minus | 82.5% | B− |
| 30 | 4 | Plus-minus | 86.7% | B |
| 10 | 1 | Plus-minus | 90% | A− |
| 50 | 0 | Plus-minus | 100% | A+ |
| 8 | 1.5 | Plus-minus | 81.3% | B− |
| 20 | 20 | Plus-minus | 0% | F |
| 20 | 2 | Simple A–F | 90% | A |
| 20 | 9 | Simple A–F | 55% | F |
Check a grade on your own
On the plus-minus scale, values run A+ 97, then A 93 · A− 90, then B+ 87 · B 83, then B− 80 · C+ 77, then C 73 · C− 70, then D+ 67 · D 63 · D− 60. Anything below 60 gets an F.
F is anything below the lowest cut-off.
Cut-offs must go down from A+ to D−.
Scoring chart for a 20-question test
| Wrong | Right | Percent | Grade |
|---|---|---|---|
| 0 | 20 | 100% | A+ |
| 1 | 19 | 95% | A |
| 2 | 18 | 90% | A− |
| 3 | 17 | 85% | B |
| 4 | 16 | 80% | B− |
| 5 | 15 | 75% | C |
| 6 | 14 | 70% | C− |
| 7 | 13 | 65% | D |
| 8 | 12 | 60% | D− |
| 9 | 11 | 55% | F |
| 10 | 10 | 50% | F |
| 11 | 9 | 45% | F |
| 12 | 8 | 40% | F |
| 13 | 7 | 35% | F |
| 14 | 6 | 30% | F |
| 15 | 5 | 25% | F |
| 16 | 4 | 20% | F |
| 17 | 3 | 15% | F |
| 18 | 2 | 10% | F |
| 19 | 1 | 5% | F |
| 20 | 0 | 0% | F |