How to Grade a Test: Percentage Formula, Chart and Curves
Turning a raw score into a percentage takes one division. The harder part is everything around it: curving a test that went badly, handling extra credit, scoring partial credit, and deciding what to do with 79.5%. This guide covers each one with worked numbers you can check yourself.
Quick answer: test grade % = points earned ÷ points possible × 100. 42 out of 50 is 84%, a B. 17 out of 20 is 85%, a B, because each question on a 20-question test is worth 5%.
Grading rules differ between schools and teachers, so check your own policy before applying any of this. Last reviewed: October 2026.
The formula for a test grade percentage
A test grade is the share of the available points a student earned, written as a percentage.
Test grade (%) = points earned ÷ points possible × 100
The same formula shows up in three forms:
- Points: 42 of 50 points is 42 ÷ 50 × 100 = 84%, a B.
- Number correct: 17 of 20 questions is 85%, a B. Each question is worth 5%.
- Number wrong: 25 questions with 4 wrong means 21 correct, and 21 ÷ 25 × 100 = 84%, a B.
Counting whichever number is smaller, usually the wrong answers, is faster and less error-prone. If you would rather skip the arithmetic, a teacher grader calculator like the EZ grader does it as you type. Letter grades here use the standard plus/minus scale; the grading scale chart shows every cutoff.
Test score percentage chart (50 questions)
A quick reference for a 50-question test. Every question is worth 2%, so each wrong answer takes off 2 points.
| Correct | Wrong | Percentage | Letter |
|---|---|---|---|
| 50 of 50 | 0 | 100% | A+ |
| 48 of 50 | 2 | 96% | A |
| 45 of 50 | 5 | 90% | A- |
| 43 of 50 | 7 | 86% | B |
| 40 of 50 | 10 | 80% | B- |
| 38 of 50 | 12 | 76% | C |
| 35 of 50 | 15 | 70% | C- |
| 33 of 50 | 17 | 66% | D |
| 30 of 50 | 20 | 60% | D- |
| 25 of 50 | 25 | 50% | F |
Assumes equal question weights and no partial credit. For every score on a 50-question test, open the 50-question chart.
How many can you miss? By test length
The most wrong answers allowed to keep a given score, for common test lengths. Open a row for the full chart, which you can print, copy or download.
| Test length | Each question | Keep 90% | Keep 80% | Keep 60% |
|---|---|---|---|---|
| 8 questions | 12.5% | 0 wrong | 1 wrong | 3 wrong |
| 10 questions | 10% | 1 wrong | 2 wrong | 4 wrong |
| 12 questions | 8.33% | 1 wrong | 2 wrong | 4 wrong |
| 13 questions | 7.69% | 1 wrong | 2 wrong | 5 wrong |
| 14 questions | 7.14% | 1 wrong | 2 wrong | 5 wrong |
| 15 questions | 6.67% | 1 wrong | 3 wrong | 6 wrong |
| 16 questions | 6.25% | 1 wrong | 3 wrong | 6 wrong |
| 18 questions | 5.56% | 1 wrong | 3 wrong | 7 wrong |
| 20 questions | 5% | 2 wrong | 4 wrong | 8 wrong |
| 22 questions | 4.55% | 2 wrong | 4 wrong | 8 wrong |
| 24 questions | 4.17% | 2 wrong | 4 wrong | 9 wrong |
| 25 questions | 4% | 2 wrong | 5 wrong | 10 wrong |
| 30 questions | 3.33% | 3 wrong | 6 wrong | 12 wrong |
| 34 questions | 2.94% | 3 wrong | 6 wrong | 13 wrong |
| 40 questions | 2.5% | 4 wrong | 8 wrong | 16 wrong |
| 45 questions | 2.22% | 4 wrong | 9 wrong | 18 wrong |
| 50 questions | 2% | 5 wrong | 10 wrong | 20 wrong |
| 60 questions | 1.67% | 6 wrong | 12 wrong | 24 wrong |
| 100 questions | 1% | 10 wrong | 20 wrong | 40 wrong |
Test length not listed? The EZ grader calculator builds a chart for any number of questions.
Grading a stack of papers faster
When every paper has the same number of questions, a printed chart beats a calculator. You only count wrong answers and look up one row.
- Open the EZ grader chart for your test length, for example the 20-question chart or the 25-question chart, and print it or save it as a PDF.
- Mark each paper and write the number of wrong answers at the top.
- Look up that number and write the percentage and letter next to it.
- Re-check a few papers with the calculator, especially ones near a grade cutoff.
- Enter the final scores in your gradebook, which is the official record.
How to curve a test: three methods
A curve is a teacher's decision, not a fixed rule, and some schools restrict it. These are three methods, each with the same kind of student so you can compare them.
1. Add a flat amount
Add 5 percentage points to every score and cap the result at 100%.
| Before | After +5 (capped at 100) | Letter |
|---|---|---|
| 62% | 67% | D- → D+ |
| 82% | 87% | B- → B+ |
| 97% | 100% | A+ → A+ |
2. Fix a flawed question
Say question 7 on a 25-question test was unclear. A student has 20 correct, so 80%. Two common fixes give different results depending on whether the student got the question right.
| Student | Original | Everyone gets credit | Question removed |
|---|---|---|---|
| Missed question 7 | 20/25 = 80% | 21/25 = 84% | 20/24 = 83.33% |
| Got question 7 right | 20/25 = 80% | 20/25 = 80% | 19/24 = 79.17% |
Giving everyone credit never hurts anyone. Removing the question can lower the score of students who answered it correctly, which is worth knowing before you choose.
3. Scale to the top score
Divide each score by the highest score and multiply by 100, so the best paper becomes 100%. With a top score of 92%:
Scaled score = score ÷ top score × 100
60 ÷ 92 × 100 = 65.22% (D)
80 ÷ 92 × 100 = 86.96% (B)
92 ÷ 92 × 100 = 100% (A+)
Scaling keeps students in the same order and lifts every score in proportion. A single unusually high score can make the scale too gentle, so some teachers use a high-but-typical score instead.
How to add extra credit
Take a student with 42 of 50 points and 3 bonus points.
| Method | Calculation | Result |
|---|---|---|
| Bonus added to points earned | (42 + 3) ÷ 50 | 90% (A-) |
| Bonus also added to the total | (42 + 3) ÷ (50 + 3) | 84.91% (B) |
The first method is the usual one. The second punishes students who skip the optional work: the same student without the bonus would get 42 ÷ 53 = 79.25%, lower than the original 84%. Also decide whether scores are capped: a student with 49 of 50 plus 3 bonus points has 104%, which many teachers cap at 100%. Put the policy in the syllabus so it is the same for everyone.
How to grade partial credit
With partial credit, grade in points, not in questions. Add up the points earned on every question, then divide by the points possible. Here are ten questions worth 4 points each (40 points in total):
4 + 4 + 3 + 2 + 4 + 4 + 1 + 4 + 3.5 + 2 = 31.5 points
31.5 ÷ 40 × 100 = 78.75% (C+)
Half points are fine too. The calculator and the half-point charts on each chart page work in 0.5 steps.
From one test to a course grade: weighted categories
A test is usually one part of a course grade. Courses often weight categories differently, so a simple average of every score is the wrong number. Multiply each category average by its weight, add the results, and divide by the total weight.
Homework: 90 × 20 = 1800
Quizzes: 85 × 30 = 2550
Exams: 88 × 50 = 4400
Total ÷ 100 = 87.5% (B+)
The average grade calculator does this for any number of categories, and the final grade calculator shows what a student needs on the last exam.
Rounding and borderline scores
A score of 79.5% lands right on the edge. Whether it counts as 80% depends entirely on your policy:
| Score | Plus/minus scale | 10-point scale |
|---|---|---|
| 79.5% (not rounded) | C+ | C |
| 80% (rounded up) | B- | B |
If you round, round once at the end, never the percentage before you check the cutoff, because that can move a student across a line they have not really crossed. Whatever you choose, apply it to everyone. More on this in the borderline grades section of the grading scale chart.
Mistakes that give the wrong grade
- Entering wrong answers as correct (or the other way round). Check which number you typed.
- Using the wrong total. If questions are worth different points, divide by total points, not the number of questions.
- Removing a flawed question without checking who it helps. See the table above: removing can lower scores.
- Rounding too early. Round once at the end.
- Averaging percentages from tests of different sizes. Add the points instead, or weight the categories.
If a student questions a grade
Most disputes come down to arithmetic, rounding or a missing score. Working through it the same way each time keeps it calm and fair:
- Find the exact point of disagreement: a point tally, rounding or a missing assignment.
- Recalculate the score from points earned and points possible.
- Check the school's official rounding and grade-boundary policy.
- Review category weights and any missing work entries.
- Share the arithmetic so the student can follow it, and correct the record if there was a mistake.
Frequently asked questions
How do you calculate a test grade percentage?
Divide the points earned by the points possible and multiply by 100. For example, 42 out of 50 is 42 ÷ 50 × 100 = 84%, which is a B on the standard plus/minus scale.
What grade is 17 out of 20 on a test?
17 out of 20 is 85%, a B on the standard plus/minus scale. Each question on a 20-question test is worth 5%, so 3 wrong answers cost 15 points.
How many questions can you miss and still get an 80%?
It depends on the length of the test. You can miss 4 of 20, 5 of 25, 6 of 30, 10 of 50, or 20 of 100. The rule is 20% of the questions, rounded down.
How do you work out what each question is worth?
Divide 100 by the number of questions. A 20-question test is 5% per question, 25 questions is 4% and 40 questions is 2.5%. If questions have different point values, divide each question's points by the total points instead.
How do you curve a test?
Three methods teachers use are adding a flat amount (for example 5 points, capped at 100), giving everyone credit for a flawed question, and scaling scores so the highest becomes 100. On a 25-question test, a student with 20 correct who missed a flawed question goes from 80% to 84% if everyone gets credit. Removing the question instead gives 83.33%, and lowers the score of a student who got it right to 79.17%. Follow your school's policy.
How do you grade a test with partial credit?
Add up the points a student earned on every question, then divide by the total points possible. For example, 31.5 points out of 40 is 78.75%, a C+.
How does extra credit work?
The simplest method adds the bonus points to the points earned and leaves the total unchanged. With 42 of 50 and 3 bonus points, the score is 45 ÷ 50 = 90%. Some teachers cap the score at 100%. Adding the bonus to the total as well (45 ÷ 53) lowers the score of students who skip it, so check your policy.
Does 79.5% round up to 80%?
Only if your instructor rounds. Unrounded, 79.5% is a C+ on the plus/minus scale and a C on a 10-point scale. Rounded to 80%, those become a B- and a B. Check the syllabus, and round once, at the end.
What is a teacher grader calculator?
A teacher grader calculator, also called an EZ grader or easy grader, turns the number of questions on a test and the number a student missed into a percentage and letter grade. The EZ grader calculator on this site works for any test length, with half points and a choice of grading scale.
How can I grade a stack of papers faster?
Print the chart for your test length, count the wrong answers on each paper, and read the percentage and letter from one row. Spot-check a few papers with the calculator, especially ones near a grade cutoff, then enter the final scores in your gradebook.
What should I do if a student disputes a grade?
Recalculate the score from the points earned and points possible, check the school's rounding and grade-boundary policy, and review any weighted category rules and missing work. Show the arithmetic so the student can follow it.