Example class: eight made-up scores, with ten flat points added. Paste yours over them, or
Grade curve calculator
Paste your class scores and see what each curve changes, score by score, before you apply one.
Letter scale: Common US plus/minus scale
The plus/minus cutoffs Wikipedia lists for US colleges: A+ from 97%, A 93, A- 90, B+ 87, B 83, B- 80 and so on down to D- at 60. It is not universal, so use your syllabus's cutoffs when they differ. Source: Wikipedia, “Academic grading in the United States”.
| Letter | Lowest % | Remove |
|---|
Each letter starts at its lowest percentage and runs up to the next letter.
Rounding and decimal places
Follow your syllabus. A displayed percentage can round up while the unrounded score stays below a cutoff.
Only changes how results are shown. Extra places appear when rounding would push a score over a letter cutoff.
A letter typed as a score counts as the lowest percentage for that letter on this scale. Use the original percentage when you have it.
Check a single cutoff with the grading scale calculator.
Compare the whole class
| Method | Mean | Lowest | Highest |
|---|---|---|---|
| Add flat points (10 points) | 79.38% | 58% | 100% |
| Add enough to bring the top score to 100 | 79.38% | 58% | 100% |
| Multiply so the top score becomes 100 | 77.08% | 53.33% | 100% |
| Square-root curve | 82.9% | 69.28% | 94.87% |
| Shift to a target mean (0% target) | 5.56% | 0% | 20.63% |
| Bell curve (mean 0%, spread 0) | 0% | 0% | 0% |
Every score, before and after
| Paper | Before | After | Letter | Rank before → after |
|---|---|---|---|---|
| 1 | 62% | 72% | C- | 6 → 6 |
| 2 | 71% | 81% | B- | 4 → 4 |
| 3 | 55% | 65% | D | 7 → 7 |
| 4 | 84% | 94% | A | 2 → 2 |
| 5 | 48% | 58% | F | 8 → 8 |
| 6 | 77% | 87% | B+ | 3 → 3 |
| 7 | 90% | 100% | A+ | 1 → 1 |
| 8 | 68% | 78% | C+ | 5 → 5 |
Grading scales checked . Sources are at the bottom of the page.
What the formulas change
Add flat points: add the entered number to every score. Bring the top to 100 by addition: add the gap between the highest score and full credit. Both preserve score gaps until capping changes them.
Scale the top to 100: multiply every score by 100 divided by the highest score. Square root: take the square root of each percentage, then multiply by ten. Check that this is the curve your instructor chose before changing scores.
Target mean: add the difference between the target mean and the current mean. Without capping, the adjusted mean meets the target. With capping, it may not.
Bell curve: each score keeps its distance from the class mean, counted in standard deviations (its z-score), and is placed the same distance from the target mean at the target spread. In a class of 50, 60 and 70 the mean is 60 and the spread is about 8.16 points, so the 70 sits about 1.22 standard deviations above. With a target mean of 75 and a spread of 5, it becomes about 81.1, the 60 becomes 75 and the 50 about 68.9. The spread is the whole class's standard deviation. A class where every score is the same has no spread, so the tool asks for a flat curve instead.
A curve is a policy decision
The calculations do not tell you which curve is fair or appropriate. Use the rule the instructor or department actually chose. Without capping, some methods can produce scores outside the usual percentage range.
The example class averages 69.375%. Adding ten points gives 79.375%. Scaling the top score instead changes the gaps between students. The table shows ranks and ties for the selected method.
The bell curve here rescales scores; the letters then come from your grading scale. Grading by rank, where a fixed share of the class gets each letter, is a different policy, and this tool does not do it. For a plain score before any curve, use the easy grader. To change letter boundaries instead, use the grading scale calculator.