Free grading calculator
Test Curve Calculator
Paste every student's raw score, choose a curve method and compare each grade before and after. Try different methods to see which one fits your situation.
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Test curve calculator
Class average: 71% before, 79% after the curve.
| Score | Before | After | Grade change |
|---|---|---|---|
| 46/50 | 92% | 100% | A- → A+ |
| 42/50 | 84% | 92% | B → A- |
| 40/50 | 80% | 88% | B- → B+ |
| 39/50 | 78% | 86% | C+ → B |
| 37/50 | 74% | 82% | C → B- |
| 35/50 | 70% | 78% | C- → C+ |
| 33/50 | 66% | 74% | D → C |
| 31/50 | 62% | 70% | D → C- |
| 28/50 | 56% | 64% | F → D |
| 24/50 | 48% | 56% | F → F |
The four curve methods compared
| Method | How it works | Best for |
|---|---|---|
| Raise the top score to 100% | Finds the gap between the top score and 100% and adds it to everyone. | A test that was a little too hard for the whole class. |
| Scale (multiply) | Divides every score by the top score, so the top paper becomes 100% and everyone else rises in proportion. | Keeping the ranking and the gaps in proportion. Higher scores gain more points. |
| Square root | Takes the square root of each percentage and multiplies by 10. A 64% becomes 80%; a 100% stays 100%. | Helping low scores most without pushing anyone over 100%. |
| Flat bonus | Adds the same number of percentage points to everyone, capped at 100%. | Making up for one flawed question worth a known number of points. |
Worked example
The calculator starts with ten scores on a 50-point test. The top score is 46/50, or 92%. "Raise the top score to 100%" adds 8 points to everyone, so the class average goes from 71% to 79%. Switch the method to square root and the 48% at the bottom rises to about 69%, while the 92% only rises to about 96%: the square root curve helps the students who struggled most.
Before you curve, look at why the scores were low. If most of the class missed the same question, the fairest fix is often to remove that question (see how to handle a bad test question), not to curve the whole test.
Test curve calculator FAQ
What is the fairest way to curve a test?
There's no single fairest method. Adding points so the top score reaches 100% is simple and keeps every gap between students the same. The square root curve helps low scores most. If one question was flawed, removing it is usually fairer than any curve.
How does the square root curve work?
Take the square root of the percentage and multiply by 10. A 49% becomes 70%, a 64% becomes 80% and an 81% becomes 90%. A 100% stays 100%, so no one goes over the maximum.
Can a curve lower a student's grade?
Not with these methods. All four only raise or keep scores. A bell-curve system that assigns a fixed share of each letter grade can lower grades, which is one reason most K-12 teachers avoid it.
Should I tell students I curved the test?
Yes. Explain the method and why you used it. Students accept a curve much more readily when they understand it applied to everyone equally.