The short answer
Test percent = (total − wrong) ÷ total × 100. On a 40-question test, 6 wrong is 34 ÷ 40 = 85% (B). Each question is worth 2.5%, so you can miss 2 for an A (93%), 4 for an A−, 6 for a B and 10 for a C on the standard plus/minus scale.A test comes back with “−6” at the top. What is that as a percent, and is it still a B? This calculator answers that and the question that usually comes next: how many could you have missed for the next letter up?
The test score formula
Percent = (total − wrong) ÷ total × 100. If you know points earned instead of the number wrong, it’s points earned ÷ points possible × 100.
Worked example: a 40-question test, 6 wrong.
- Correct answers: 40 − 6 = 34.
- Divide by the total: 34 ÷ 40 = 0.85.
- Multiply by 100: 85%, a B on the standard plus/minus scale.
Each question on a 40-question test is worth 100 ÷ 40 = 2.5%. That “value of one question” is shown under the result, and it is the quickest way to think about a test: on a 20-question quiz each one is 5%, on a 50-question test each one is 2%.
How many can you miss? A quick table
The numbers below come straight from the formula: the most you can miss is total × (1 − cutoff ÷ 100), rounded down. They use the standard plus/minus cutoffs without rounding.
| Questions | A (93%) | A− (90%) | B (83%) | B− (80%) | C (73%) | C− (70%) | D− (60%) |
|---|---|---|---|---|---|---|---|
| 10 | 0 | 1 | 1 | 2 | 2 | 3 | 4 |
| 20 | 1 | 2 | 3 | 4 | 5 | 6 | 8 |
| 25 | 1 | 2 | 4 | 5 | 6 | 7 | 10 |
| 30 | 2 | 3 | 5 | 6 | 8 | 9 | 12 |
| 40 | 2 | 4 | 6 | 8 | 10 | 12 | 16 |
| 50 | 3 | 5 | 8 | 10 | 13 | 15 | 20 |
| 100 | 7 | 10 | 17 | 20 | 27 | 30 | 40 |
Short quizzes are unforgiving: on a 10-question quiz, a single miss drops you from 100% to 90%, and there’s no room for an A at 93%. Longer tests give you more room per letter.
Points, half credit and different scales
Not every test is one point per question. Switch to Points earned for tests with mixed point values, partial credit or a written section. Enter the total points and the points you got — half points such as 47.5 are fine. When you switch modes, the calculator converts your entry so the score stays the same.
The grading scale menu changes the letters, not the percent:
- Standard plus/minus: A 93, A− 90, B+ 87, B 83 and so on.
- 10-point: A 90, B 80, C 70, D 60.
- 7-point: A 93, B 85, C 77, D 70 — the same 85% that’s a B on the 10-point scale is a B here too, but an 84% is a C.
The full table (open it under the calculator) lists every possible number wrong with its percent and letter, and highlights your row.
What is 17 out of 20? Common test scores with half points
Most “what grade is this?” questions are about the same handful of test lengths. The table converts typical raw scores, including half points, with the test score formula: points earned ÷ points possible × 100. Letters use the standard plus/minus scale with no rounding.
Common test scores as a percent and letter grade (standard plus/minus scale)
| Score | Percent | Letter | One point is worth |
|---|---|---|---|
| 15 / 20 | 75% | C | 5% |
| 17 / 20 | 85% | B | 5% |
| 18.5 / 20 | 92.5% | A− | 5% |
| 19 / 25 | 76% | C | 4% |
| 21 / 25 | 84% | B | 4% |
| 22.5 / 25 | 90% | A− | 4% |
| 26.5 / 30 | 88.3% | B+ | 3.33% |
| 34 / 40 | 85% | B | 2.5% |
| 36.5 / 40 | 91.3% | A− | 2.5% |
| 43 / 50 | 86% | B | 2% |
| 43.5 / 50 | 87% | B+ | 2% |
| 89.5 / 100 | 89.5% | B+ (A− if rounded) | 1% |
Two patterns are worth knowing. First, half a point can change the letter: 43 out of 50 is a B, while 43.5 is a B+, because the B+ cutoff sits at exactly 87%. Second, the “one point is worth” column is the quickest way to calculate test grades in your head. On a 25-point quiz, every point you lose costs 4%, so losing 2.5 points leaves 90%.
To see what that score does to your class average, put it into the class grade calculator with categories. If your teacher grades whole stacks with a printable easy grading chart, that chart uses the same formula, so the percents will match.
Partial credit, bonus questions and dropped questions
Three situations trip up the simple formula:
- Partial credit. If a 4-point question earned 2.5 points, “number wrong” stops making sense. Use Points earned and add up what you actually got.
- Bonus questions. Extra-credit points go into “points earned,” not into the total. On a 50-point test with a 5-point bonus, 52 points is 104%. The calculator won’t accept more earned than possible, so in that case enter the score your teacher recorded, or work it out by hand: earned ÷ regular total × 100.
- Thrown-out questions. If the teacher drops a broken question for everyone, the total shrinks. A 40-question test with one question removed is out of 39. If you had 6 wrong and the removed question was one you got right, that’s 33 ÷ 39 = 84.6%; if it was one you missed, it’s 5 wrong, or 34 ÷ 39 = 87.2%.
In each case, check the score in the gradebook afterward — the portal shows what was actually recorded.
What one test does to your class grade
A test score on its own isn’t your grade. How much an 85% matters depends on the category it lands in and how many other tests share that category. To see the effect, enter the test in the grade calculator and use its what-if box. Before a final, the final grade calculator shows the score you need for the grade you want.
Related tools
- Teachers making an answer-key chart for a whole class: the EZ Grader.
- Average several test scores at once: the average grade calculator.
- Scores came out low across the class? The grade curve calculator compares curving methods.
- Other scales and GPA points: the grading scale converter.
Frequently asked questions
How do I calculate my test score as a percentage?
How many questions can I miss and still get an A?
What if questions are worth different points?
Does my teacher round test scores?
What's the difference between this and the EZ Grader?
What is 17 out of 20 as a grade?
What percent is a B on a test?
How do I calculate a test grade with half points?
Sources & method
- Formula: (total − wrong) ÷ total × 100; maximum misses = floor(total × (1 − cutoff ÷ 100)), computed in your browser.
- Scales: standard US plus/minus (A+ 97, A 93, A− 90 … D− 60), 10-point (90/80/70/60) and 7-point (93/85/77/70). Your school’s scale may differ — see the grading scale converter.
Formulas checked October 2026. Spotted an error? Tell us via the about page.