A grade curve calculator applies a statistical curve to adjust class scores — raising the class average, reducing the impact of an overly difficult exam, or forcing a target grade distribution. Visual histograms show before/after distributions so you can preview the effect before finalizing grades.
Enter Student Grades
Before vs After Statistics
Before Curve
After Curve
Individual Grade Changes
| # | Raw Grade | Curved Grade | Change | Letter |
|---|
How to Use the Grade Curve Calculator
Grading curves allow teachers to adjust scores when an exam was harder than intended, or to create a target grade distribution across a class. This calculator supports four curve types and shows visual histograms so you can preview the exact effect before applying it to your gradebook.
Step 1: Enter Grades
Paste your class scores into the text area — separated by commas, spaces, or line breaks. Scores should be on a 0-100 scale. Click Load Grades to parse and validate them. You'll see the raw class statistics (count, mean, median, standard deviation) immediately. Use Load Example to see a sample class of 30 students.
Step 2: Choose Curve Type
Linear Shift: Adds a fixed number of points to every score. Simplest curve — the class average rises by exactly the points added. Best when the exam was slightly harder than intended across the board.
Square Root: Uses √(score/100) × 100. Lifts low scores significantly more than high scores — a 49 becomes a 70, but a 90 becomes a 95. Best when the lower half of the class struggled but you want to preserve separation at the top.
Bell Curve: Forces a target grade-letter distribution by ranking students and assigning letters based on percentile cutoffs. Set your target percentages for A, B, C, D, and F. Best for large classes where a standard distribution is the grading policy.
Custom Scale: Scales all grades so the top scorer receives 100. Enter the highest raw score in the class — every other grade is scaled proportionally. Best when an exam was simply too hard and the best student got an 82 instead of 100.
Step 3: Review Results
The results show side-by-side statistics (mean, median, standard deviation before and after), dual histograms, and a table of every student's raw vs curved grade with letter grades. Export to CSV for pasting into your gradebook.
FAQ
Is this grade curve calculator free?
Yes, completely free with no ads or signup. All grade processing happens in your browser. No student data is sent to any server.
Is student grade data private?
Yes. All grade data is processed locally in your browser only. Nothing is stored or transmitted. This tool handles no personally identifiable information.
What is a linear grade curve?
A linear curve adds a fixed number of points to every student's grade. If you add 7 points, a 73 becomes an 80, a 55 becomes a 62. This is the simplest curve and treats all students equally — the class average rises by exactly the points added, and the grade distribution shape stays the same.
How does the square root curve work?
The square root curve uses the formula: new grade = √(raw grade / 100) × 100. For example, a 64 becomes √(0.64) × 100 = 80. This curve benefits lower-scoring students more than high scorers. A 100 stays 100, while a 49 becomes a 70. It compresses the lower end of the distribution upward.
What is a forced bell curve and when should I use it?
A forced bell curve assigns grade letters based on class rank to hit target percentages — typically A: 10%, B: 25%, C: 30%, D: 25%, F: 10%. This is controversial because students are graded relative to each other, not absolute mastery. It works in large introductory courses where grade inflation is a concern and a standard distribution is expected.
What is the custom high-score curve?
The custom curve scales all grades proportionally based on the highest score in the class. If the top score is 87, the new formula is: new grade = (raw / 87) × 100. The top student gets 100%, and all other grades scale up proportionally. This is useful when a test was unexpectedly difficult and the highest achievable score was well below 100.
How do I enter student grades?
You can type grades one at a time using the Add Grade button, or paste a list of numbers separated by commas, spaces, or line breaks into the text area. Grades should be on a 0-100 scale. The calculator accepts decimals (e.g., 87.5).