Grade Curve Calculator
Paste a class's scores, pick a curve — a flat boost, a square-root curve or scaling the highest score to 100 — and see every grade before and after, with the class average and how far it moves. Copy the curved list when you are happy with it. Free, no sign-up.
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Curve method
Curved grades stop at 100. A score already at or above 100, such as extra credit, is left as entered.
How to Use the Grade Curve Calculator
- 1. Paste the scores. Put one grade per line, or separate them with commas. Non-numbers and negative values are ignored, and a counter shows how many scores were read.
- 2. Choose a curve. Flat boost asks for the number of points to add (5 to start). Square-root curve and Scale highest to 100 need no setting.
- 3. Compare. The cards show the average before and after, the average change and the highest score before the curve. The table lists every grade with its original value, curved value and change.
- 4. Copy the result. Copy Curved List puts the curved grades on your clipboard, one per line to one decimal place, ready for a spreadsheet or gradebook.
The Three Curves, Side by Side
Take seven scores: 52, 61, 68, 74, 79, 85 and 91, with an average of 72.9. Here is what each method does to them.
| Original | Flat +5 | Square root | Scale top to 100 |
|---|---|---|---|
| 52 | 57.0 | 72.1 | 57.1 |
| 61 | 66.0 | 78.1 | 67.0 |
| 68 | 73.0 | 82.5 | 74.7 |
| 74 | 79.0 | 86.0 | 81.3 |
| 79 | 84.0 | 88.9 | 86.8 |
| 85 | 90.0 | 92.2 | 93.4 |
| 91 | 96.0 | 95.4 | 100.0 |
| Average 72.9 | 77.9 (+5.0) | 85.0 (+12.2) | 80.1 (+7.2) |
- Flat boost adds the same points to everyone and stops each grade at 100. Gaps between students stay the same, except for anyone who hits the cap. It is the simplest to explain and the easiest to defend.
- Square-root curve turns each grade into 10 × √grade. It gives the most to low scores — 52 gains over 20 points, 91 gains under 5 — and a 100 stays 100. It squeezes the whole class toward the top, which is generous: here the average rises more than 12 points.
- Scale highest to 100 multiplies every grade by 100 ÷ the top score (here 100 ÷ 91). The best student gets 100 and everyone rises by the same percentage, so higher scores gain more points than lower ones. It rewards a hard test without changing the ranking.
Choosing a Method — and What This Tool Doesn't Do
Use a flat boost when the whole test was a little too hard or one question was bad. Use scaling when the best score is unusually low and you want to anchor the top at 100. Use the square root only if you want a large, generous lift. Whichever you pick, the order of students never changes: every method here is monotonic.
"Grading on a curve" has two meanings. This calculator adjusts raw scores. It does not do the other kind, where letter grades are assigned by rank or by distance from the class mean — for example a fixed share of As and Bs. For that, standardise the scores with the Z-Score Calculator or the Standard Score Converter, and look at where each student sits against the average.
Two limits to know. Every curve here stops at 100, and a score already at or above 100, such as extra credit, is left as entered rather than pulled down. And a curve does not make the test fair after the fact: if many students missed the same question, check the question before curving.
Which Tool Do You Need?
| You want to | Use |
|---|---|
| Adjust a list of raw scores | This Grade Curve Calculator |
| Rank students and find class percentile | Class Rank Calculator |
| See the mean and spread of the scores first | Statistics Calculator |
| Turn a percentage into a letter grade | Letter Grade Calculator |
Frequently Asked Questions
- What is a square-root curve?
- A square-root curve replaces each grade with 10 times the square root of the original score, so a 49 becomes a 70 and an 81 becomes a 90. It lifts low scores the most — a 25 becomes a 50 — while leaving a 100 unchanged.
- How does a flat boost curve work?
- A flat boost adds the same number of points to every grade, capped at 100. It shifts the class average up by the boost, except when some scores hit the cap, and it keeps the gaps between students the same.
- What does scaling the highest score to 100 do?
- Every grade is multiplied by 100 divided by the highest score in the list. If the top score was 92, all grades are multiplied by 100 ÷ 92, so the best student gets 100 and everyone else rises in proportion.
- Which curve helps low scores the most?
- The square-root curve. It adds the most points at the bottom — a 25 gains 25 points while a 90 gains under 5 — which narrows the gap between struggling and strong students more than a flat boost or proportional scaling.
- How do I curve a test in Excel or Google Sheets?
- Use the same formulas in a column:
=MIN(100, A2 + 5)for a flat boost,=10*SQRT(A2)for the square-root curve, and=A2*100/MAX(A:A)for scaling the top score to 100. This calculator gives the same numbers, and the copy button pastes them back. - Is curving grades fair?
- It is a judgement call that belongs to the instructor. A curve can correct a test that was too hard, but it can also reward a weak class or hide a poor question. Tell students which method you use and apply the same rule to everyone.