On a 20-question test you can miss 8 questions and still pass at 60%, 5 and still earn a C, or 3 and still earn a B. To get an A you can only miss 1 question, because an A needs at least 19 correct.
The missed-question limit for every grade
A 20-question test is the most common paper length in US schools, and it is also the easiest to reason about because every question is worth exactly 5 percentage points.
Work out the required correct answers first, then subtract them from 20 to get the number you can afford to miss.
| Letter grade | Minimum percentage | Correct needed | Most you can miss |
|---|---|---|---|
| A | 93% | 19 | 1 |
| A− | 90% | 18 | 2 |
| B+ | 87% | 18 | 2 |
| B | 83% | 17 | 3 |
| B− | 80% | 16 | 4 |
| C+ | 77% | 16 | 4 |
| C | 73% | 15 | 5 |
| C− | 70% | 14 | 6 |
| D+ | 67% | 14 | 6 |
| D | 63% | 13 | 7 |
| D− | 60% | 12 | 8 |
| F | below 60% | 11 or fewer | 9 or more |
How the maths works
Multiply the test length by the passing percentage, round the answer up to a whole question, then subtract that from the total.
- For a pass at 60%: 20 × 0.6 = 12 correct, so 20 − 12 = 8 questions can be missed.
- For a B at 83%: 20 × 0.83 = 16.6, which rounds up to 17 correct, so 3 questions can be missed.
- For an A at 93%: 20 × 0.93 = 18.6, which rounds up to 19 correct, so only 1 question can be missed.
Why rounding up matters
Half a question cannot be answered correctly, so the required correct answers always round up. Rounding down would hand out a grade the test length cannot actually produce.
That is why a C+ on a 20-question test is impossible to earn: it needs 15.4 correct answers, and neither 15 nor 16 lands inside the 77% to 79% band.
Check another test length
The same method works for any paper. Use the grading scale for 20 questions for the full wrong-answer chart, or the grade chart generator to build one for a different length.
Frequently Asked Questions
How many questions can you miss out of 20?+
You can miss 8 and still pass at 60%. For a C you can miss 5, for a B three, and for an A only one.
What score is 8 wrong out of 20?+
Eight wrong out of 20 leaves 12 correct, which is exactly 60%, a D− and the lowest passing grade.
How many can you miss to get a 70?+
A 70% (a C−) allows 6 wrong answers, leaving 14 correct.
Is 20 questions a lot for a test?+
It is the most common short-test length. Because each question is worth 5 percentage points, letter bands fall unevenly and several grades, such as C+, cannot be reached.
Muhammd Salman
I build and maintain Grade Calculator independently. Every worked example on this site is checked against the underlying formula, with notes on where school or instructor policy can change the result. More about this site →