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Formula
Test score (%) = (total − wrong) ÷ total × 100
- total
- number of questions, or total points when questions are worth different amounts
- wrong
- questions missed or points taken off (enter the number right instead if that is easier)
From questions missed to a percentage
When a test comes back marked “−6”, the first question is what that means as a grade. A test grade calculator answers it from two numbers: how many questions or points the test had, and how many were wrong. It returns the percentage, the letter grade, the value of each question, and a chart of every score the test could produce.
Teachers use the chart the way they used paper “easy grader” slides: count the wrong answers on a paper, look up the row, write the grade.
How to use the calculator
- Total questions or points: the number of questions if all are worth the same, otherwise the total points.
- Number: how many were wrong, or how many were right.
- That number is: choose Wrong or Right to match what you entered.
The result shows the score, the letter grade, the number correct out of the total and how much each question is worth. For tests up to 200 questions or points, a grading chart lists the score for 0, 1, 2 … wrong all the way down.
How to calculate a test grade percentage by hand
The arithmetic takes two steps.
- Number right = total − wrong.
- Score = right ÷ total × 100.
On a 25-question test with 4 wrong: 25 − 4 = 21 right, and 21 ÷ 25 × 100 = 84%, a B on the standard scale.
When questions carry different points, do the same with points. A 35-point test where the student lost 3.5 points earns 31.5 ÷ 35 × 100 = 90%, an A−. This is the easiest way to calculate a test grade with half points: switch from counting questions to counting points.
A useful shortcut: each question is worth 100 ÷ total percent. On a 20-question test each miss costs 5%, so 3 wrong is 100 − 15 = 85%.
Score by number wrong
| Questions | Each worth | 1 wrong | 2 wrong | 3 wrong | 4 wrong | 5 wrong |
|---|---|---|---|---|---|---|
| 10 | 10% | 90% | 80% | 70% | 60% | 50% |
| 15 | 6.67% | 93.33% | 86.67% | 80% | 73.33% | 66.67% |
| 20 | 5% | 95% | 90% | 85% | 80% | 75% |
| 25 | 4% | 96% | 92% | 88% | 84% | 80% |
| 30 | 3.33% | 96.67% | 93.33% | 90% | 86.67% | 83.33% |
| 40 | 2.5% | 97.5% | 95% | 92.5% | 90% | 87.5% |
| 50 | 2% | 98% | 96% | 94% | 92% | 90% |
| 100 | 1% | 99% | 98% | 97% | 96% | 95% |
Short quizzes are unforgiving: on a 10-question quiz two mistakes already drop a student to a B−. On a 50-question exam the same two mistakes still leave a 96%.
Letter grades
The letter comes from a common US plus/minus scale: A+ from 97%, A from 93%, A− from 90%, B+ from 87%, B from 83%, B− from 80%, and so on down to D− at 60%, with F below 60%. Cutoffs are applied to the exact score, so 89.9% is a B+ unless your teacher rounds. If your school uses a different scale (some put the A at 94% or a D at 65%), read the letter from your own scale and use the percentage here.
For teachers grading a stack of tests
- Enter the test length once and keep the chart on screen; the score for any paper is one look-up.
- For tests with mixed point values, total the points per paper and enter points instead of questions.
- To curve a test, the percentage calculator helps with adding a flat percentage or scaling scores.
- To combine several test scores into a term grade, use the grade calculator.
For students checking a score
- Turn the mark on the paper into a percentage, then see how it moves your class grade in the tests category.
- Before the next exam, the final grade calculator shows what you need on it to reach your target.
Common mistakes
- Dividing wrong by total. 6 ÷ 40 = 15% is the share you missed, not your score; the score is 85%.
- Counting questions when points differ. A missed 5-point essay is not the same as a missed 1-point question.
- Forgetting partial credit. Half points matter on short tests; enter them as decimals.
- Assuming one scale. A 92% is an A− here, but an A at schools that start the A at 90%.
Glossary
- Raw score: the number of questions or points correct.
- Percentage score: raw score ÷ total × 100.
- Partial credit: points awarded for a partly correct answer.
- Grading chart: a table of scores for every possible number wrong on one test.
Worked examples
Missing 7 on a 30-question quiz
A 30-question quiz with 7 answers wrong.
Inputs: Total questions or points = 30; Number = 7; That number is = Wrong (missed)
Correct = 30 − 7 = 23 Score = 23 ÷ 30 × 100 = 76.67%
Answer: 23 out of 30 correct (7 wrong) is 76.67%, a C.
52 right on a 60-point test
A test worth 60 points where 52 points were earned.
Inputs: Total questions or points = 60; Number = 52; That number is = Right (correct)
Correct = 60 − 8 = 52 Score = 52 ÷ 60 × 100 = 86.67%
Answer: 52 out of 60 correct (8 wrong) is 86.67%, a B.
Edge case: partial credit
A 25-point test with 2.5 points taken off for partial answers.
Inputs: Total questions or points = 25; Number = 2.5; That number is = Wrong (missed)
Correct = 25 − 2.5 = 22.5 Score = 22.5 ÷ 25 × 100 = 90%
Answer: 22.5 out of 25 correct (2.5 wrong) is 90%, a A−.
Assumptions and limitations
- Every question is worth the same, or you enter points instead of questions so that each point is worth the same.
- Partial credit is allowed; enter half or quarter points (for example 2.5 wrong).
- Bonus questions and extra credit are not added on top; the score cannot exceed 100%.
- Letters follow a common US 10-point plus/minus scale (A+ 97%, A 93%, A− 90%, B+ 87% … D− 60%, F below 60%), applied without rounding. Use your own cutoffs if your school differs.
- The grading chart lists every whole number wrong for tests of up to 200 questions or points.
Frequently asked questions
How do you calculate a test grade?
Subtract the number wrong from the total to get the number right, divide by the total and multiply by 100. Missing 4 on a 25-question test gives 21 ÷ 25 × 100 = 84%.
How much is each question worth?
100 divided by the number of questions. On a 20-question test each question is worth 5%, on a 30-question test 3.33%, and on a 50-question test 2%.
How do I calculate a test grade with half points?
Treat the test as points and enter the points taken off, including halves. A 35-point test with 3.5 points off is 31.5 ÷ 35 × 100 = 90%.
How many can I miss and still get a 70%?
Thirty percent of the questions, rounded down. That is 3 on a 10-question test, 6 on 20, 9 on 30 and 15 on 50. The grading chart in the result shows the exact cutoff for any test length.
Can teachers use this as an easy grader chart?
Yes. Enter the number of questions and the chart lists the percentage and letter for every possible number wrong, which you can keep beside a stack of papers or print from the page.
What if questions have different point values?
Enter the total points as the total and the points missed as the number wrong. The formula is the same once everything is in points.
Sources
- Grade Scale — Hobart and William Smith Colleges, Department of Mathematics and Computer Science. Checked October 10, 2026.