Grade Curve Calculator
How to use the calculator
- Paste your scores in the box on the left. Names are ignored, so a whole spreadsheet column works.
- Pick a curve method. Each one is explained below.
- Copy the Curved column.
- Paste it into your spreadsheet. One score per line, same order.
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Commas, spaces, or one per line. Names and other words are ignored, so you can paste a whole column. Scores are treated as percentages out of 100.
Every score becomes 100 × (score ÷ 100)k. k = 0.5 is the square root curve. Below 1 lifts marks, 1 changes nothing, above 1 pushes them down. A 100 stays 100 and a 0 stays 0 at any k.
Flat bump of +5 points, capped at 100. Class average goes from 52.3 to 57.3 across 10 scores.
- One dot per student
- The curve
- No change
- Before
- After
- 50
| # | Score | Curved | Change |
|---|---|---|---|
| 1 | 34 | 39 | +5 |
| 2 | 41 | 46 | +5 |
| 3 | 46 | 51 | +5 |
| 4 | 48 | 53 | +5 |
| 5 | 51 | 56 | +5 |
| 6 | 54 | 59 | +5 |
| 7 | 57 | 62 | +5 |
| 8 | 60 | 65 | +5 |
| 9 | 64 | 69 | +5 |
| 10 | 68 | 73 | +5 |
- Runs in your browser
- No scores are uploaded
- Free, no sign-up
- Built for Ontario marks
Four ways to curve, and what each one does to a mark
The same ten scores, four ways. The question is not which gives the biggest number. It is what each does to the bottom of your class.
1. Flat bump
Add the same points to every score. Order and gaps stay exactly as they were. Easy to explain to a student or a parent.
new score = score + points
Add 5 and a 34 becomes 39, a 68 becomes 73. Two students cross 50. The two lowest marks are still fails.
Fair when one flawed question cost everybody about that many marks.
It moves the number, not the learning. No use when the class has not learned the material yet.
2. Scale so the top score becomes 100
Divide your target by the class high, then multiply everyone by that factor. One paper sets the ceiling.
new score = score × (target ÷ highest score)
Top score 68, target 100, factor about 1.471. A 34 becomes 50, up 16. The 68 becomes 100, up 32. The students already ahead gain most.
Defensible when the test ran harder than the practice work and the top paper shows the real ceiling.
One paper decides everyone's mark. If the top score is 62, the whole class gets multiplied by about 1.6.
3. Power / square root curve
One family of curves on a single dial. k = 0.5 is the classic square root curve: it lifts the lowest marks most, barely touches the highest, and bunches the class near the top.
new score = 100 × (score ÷ 100)k
At k = 0.5 a 34 becomes 58.3, up 24.3. A 68 becomes 82.5, up 14.5. Every fail in the class disappears.
Used when a whole assessment was pitched wrong and you want to keep the order but squeeze the spread.
It changes what a mark means more than anything else here. Work that showed Level 1 lands in Level 3, and you have to defend that.
4. Rescale to a target class average
Divide the average you want by the average you have, then multiply everyone. The class average lands exactly on target.
new score = score × (target average ÷ current average)
Moving 52.3 up to 75 takes a factor of about 1.434. A 34 becomes 48.8, a 68 becomes 97.5. The student furthest behind is still failing, and the gaps grow.
Handy for testing a hunch: if the average sat at 75, what would each student's mark have to be?
Working backwards from the average you want is the wrong direction. A mark comes from the evidence, not from a target.
Curving and the Ontario report card
Why Growing Success gives you no bell curve to fit marks into.
A curve treats a mark as a position in the class. Ontario treats it as a description of the work.
Growing Success, the province's assessment, evaluation and reporting policy, puts it plainly. Ontario, like a number of other places, has:
"...moved from norm-referenced to criterion-referenced assessment and evaluation."
Growing Success: Assessment, Evaluation and Reporting in Ontario Schools, 2010, p. 19
In plain language: a mark describes the work against the curriculum expectations, not against the other students in the class. The policy adds that no set number or percentage of students is expected at any one level. Level 3 is the provincial standard to aim for, and I use that to check that my students are achieving well.
A curve moves students across level lines
In Ontario, percentage marks line up with achievement levels:
Moving a 67 to a 72 is not five points. It is a claim that the work shows Level 3, not Level 2. And in Grades 9 to 12, 50 is the mark that earns a credit. So answer that first: does their work actually show it?
What the policy does ask for
Growing Success is not anti-arithmetic. For Grades 7 to 12 a percentage mark comes from mathematical calculation and professional judgement together. Weigh the whole body of evidence, and land on the level the student most consistently shows. Professional judgement is not a loophole in the policy. It is the policy.
Use this tool when your professional judgement does not match the results in front of you.
So when is curving fair?
When what you collected is a bad measurement, not a bad result. A broken question. Material you had not taught. Fixing those is accuracy, not generosity, and the cleanest fix is often just to drop the bad question.
When is it not? When the assessment was sound and the results are simply low. Remember that by giving free marks, you are teaching students to underachieve. Keep the expectations high and push them to do their best.
Six things to try before you curve
I try to repair the mark at its source, which is far easier to explain than any curve.
- Look at the item, not the class. Count who missed what, question by question. If eight of ten missed the same one, the question is the problem.
- Drop or re-mark the broken question. Take it out of the total, or re-score it against a fairer key. I have dropped one because the diagram photocopied too dark to read. That is a repair, not a curve, and everyone understands it.
- Reteach and reassess. If the learning is the gap, teach it again and mark the second attempt. Growing Success asks for special consideration for more recent evidence.
- Ask whether the task was pitched wrong. Were the instructions clear? Did the students understand the rubric? I give mine a simplified rubric as a checklist, so they know exactly what is expected.
- Use your professional judgement on the report card grade. Growing Success asks teachers to use professional judgement in determining each student's grade. If one assignment was marked low and it is dragging down the average, you can and should adjust the grade to match your judgement of the whole body of evidence.
- Tell students exactly what you changed and why. "I threw out question 7 because it was unclear." A silent bump teaches them that marks are negotiable, and you do not want a class that expects a curve every time it does poorly.
The comment beside the mark needs the same honesty: name the strength, name the next step, keep it specific. Our high school report card comment guide walks through how.
Questions teachers ask about curving
How do I curve grades?
Pick a method, apply it to every score the same way, then check what it did to each student before you keep it. The four common methods are a flat bump, scaling so the top score becomes 100, a square root curve, and rescaling the class to a target average. Paste your scores into the calculator on this page and the chart shows you every mark before and after.
Do Ontario teachers curve grades?
It is not standard practice here. Growing Success does not describe curving as part of determining a grade. Ontario evaluation is criterion-referenced, which means a mark should describe what a student can do against the curriculum expectations, not how they placed against classmates. The policy also says there is no expectation that a set number or percentage of students will land at any one level. Repairing a mark because a question was flawed is a different thing, and that is a normal part of fair assessment.
What is a square root curve?
A square root curve replaces each score with 10 times the square root of that score, which is the same as 100 times (score divided by 100) to the power of 0.5. A 34 becomes 58.3 and a 68 becomes 82.5. It lifts the lowest marks the most and barely moves the highest ones, so it pulls the whole class together. A score of 100 stays 100 and a score of 0 stays 0. The calculator on this page has a slider for that power, so you can make the curve gentler or stronger: below 1 lifts marks, 1 changes nothing, and above 1 pushes them down.
Which curve raises the class average the most?
It depends on your numbers. On the sample class here, which averages 52.3, scaling the top score to 100 moved the average furthest, to 76.9. Rescaling to a target average of 75 gave exactly 75, the square root curve gave 72, and a flat five point bump gave 57.3. Bigger is not better. The only question that matters is whether the new number is a truer description of what students can do.
Does curving change a student's level?
It can, and that is the part to watch. In Ontario, percentage marks line up with achievement levels: 50 to 59 is Level 1, 60 to 69 is Level 2, 70 to 79 is Level 3, and 80 to 100 is Level 4. In the sample class here, a flat five point bump moved four of the ten students up a level, and two of them crossed the 50 that earns a credit. Ask whether their work really shows that level before you keep the change.
What should I do instead of curving when a whole class does badly?
Look at the assessment first. If one question was unclear, broken, or covered material you had not taught yet, drop it or re-mark it and recalculate. That is a repair, not a curve. If the learning is the gap, reteach and reassess, then let the newer evidence carry more weight, which is what Growing Success asks for when you decide a report card grade.
Where the claims on this page come from
The documents behind the claims on this page. Page numbers are the printed page.
Links checked July 2026. If a source here does not say what we say it says, tell us at /contact/ and we will fix it.
Keep the marks and the comments in one place
The gradebook this calculator was built beside: your marks, your class lists, and the report card comments in one app.