Curve the test, fairly — see every grade move.
Paste a whole class of scores, pick a curve, and watch each grade shift. Flat points, a percentage lift, the square-root curve, top-score scaling or a bell curve — all five, side by side, before and after.
- ✓Five curve types. Compare how each method treats low, middle and top scores.
- ✓Whole-class view. Averages, pass rates and the letter distribution update live.
- ✓Student or teacher. Check just your own score, or curve an entire roster.
Grade Curve Calculator
Scores are percentages (0–100). Separate them with commas, spaces or new lines.
| # | Original | Was | Curved | Now | Change |
|---|
Just checking your own score?
Enter one score to see exactly what the curve above turns it into — no full class list needed for flat, percentage and square-root curves.
Getting started
How to curve grades with this calculator
Paste the scores
Copy the class results from your gradebook or spreadsheet and paste them in — commas, spaces or one score per line all work. A single score works too.
Pick a curve type
Choose how the adjustment is calculated: the same points for all, a percentage lift, the square-root curve, scaling to the top score, or shifting the whole class to a target average.
Set the amount
Type how big the curve is — points to add, percent to boost, or the average you're aiming for. Results recalculate as you type.
Compare before & after
Read the new average, the pass rate and the letter distribution, then scan the table to see exactly who gained what — and whether anyone's letter actually changed.
Teachers: try two or three curve types on the same scores before committing. A curve that looks generous on the average can still leave your lowest scorers behind — the distribution bars make that visible at a glance.
The methods
The five curves, and who each one helps
Every curve lifts grades, but they lift them differently. The fair question isn't "how much did the average rise?" — it's "whose grade changed, and by how much?" Here's what each method in the calculator actually does.
Flat & percentage curves
A flat curve adds the same points to every score — simple, transparent, and it preserves the gaps between students exactly. A percentage boost multiplies instead, so higher scores gain more points: at +10%, a 90 gains 9 points while a 50 gains only 5.
flat: score + points · percent: score × (1 + %)Square-root curve
The most popular curve in US classrooms. Take the square root of the percentage and multiply by 10. It helps struggling students the most — a 36 becomes a 60, a 64 becomes an 80 — while a perfect 100 stays 100, so top students are never pushed past the ceiling.
curved = 10 × √(score)Scaling & bell curves
Top-score scaling stretches the whole class so the best result becomes 100 — fair when the test itself was too hard. A bell curve (mean shift) slides every score by the same amount until the class average hits your target, keeping the spread untouched.
linear: score ÷ top × 100 · bell: score + (target − average)See the math
One brutal test, three different curves
A midterm comes back with a class average of 58% — the test was harder than intended. Here is what the same five scores become under three common fixes:
| Student | Raw | Flat +8 | √ curve | Top → 100 |
|---|---|---|---|---|
| Ana | 84% | 92% | 91.7% | 100% |
| Ben | 67% | 75% | 81.9% | 79.8% |
| Cleo | 58% | 66% | 76.2% | 69.0% |
| Dev | 46% | 54% | 67.8% | 54.8% |
| Eli | 35% | 43% | 59.2% | 41.7% |
| Average | 58.0% | 66.0% | 75.3% | 69.0% |
Notice Eli, the lowest scorer: the flat curve leaves him failing at 43%, top-score scaling barely helps, but the square-root curve lifts him to 59.2% — within a point of passing. When the goal is rescuing the bottom of the class, the shape of the curve matters more than its size.
Why the square root helps the bottom
10 × √36 = 60 · 10 × √81 = 90
Square roots grow fast at the low end and slow down near the top. Going from 36 to 49 raw (13 points) is worth 10 curved points; going from 81 to 100 (19 points) is worth the same 10. Struggling students get the biggest lift per point earned, and nobody can exceed 100.
That compression is also the trade-off: gaps between top students shrink, so an 84 and a 93 end up only a few points apart after the curve.
Reference
The letter scale your curved grades land on
A curve only changes the percentage — the letter still comes from the standard US scale below. When you scan the results table, a curved score is graded against these same cutoffs.
| Letter | Percentage | GPA | What it means |
|---|---|---|---|
| A+ | 97–100% | 4.0 | Exceptional |
| A | 93–96% | 4.0 | Excellent |
| A− | 90–92% | 3.7 | Excellent |
| B+ | 87–89% | 3.3 | Above average |
| B | 83–86% | 3.0 | Good |
| B− | 80–82% | 2.7 | Good |
| C+ | 77–79% | 2.3 | Average |
| C | 73–76% | 2.0 | Average |
| C− | 70–72% | 1.7 | Below average |
| D+ | 67–69% | 1.3 | Poor |
| D | 63–66% | 1.0 | Poor |
| D− | 60–62% | 0.7 | Minimum pass |
| F | Below 60% | 0.0 | Failing |
Watch out
Curving mistakes that backfire
Curving before you check the test itself.
If half the class missed the same question, the question may be broken — fix or drop it first, then curve what's left. A curve on top of a bad item hides the real problem.Promising a curve, then shrinking it.
Students plan around what you announce. Decide the method after you see the scores, and say only that grades "may be adjusted" until then.Letting grades pass 100 without a policy.
A flat +8 turns a 96 into a 104. Decide in advance: cap at 100 (this calculator's default), or let the extra points stand as earned bonus.Using a percentage boost to help weak students.
Multiplying favors the top — at +10%, a 90 gains 9 points and a 40 gains 4. If the goal is lifting the bottom, the square-root curve or a flat add does the opposite.Curving one test but grading the course raw.
Enter the curved score into your gradebook, not the raw one — mixing the two is the most common reason a student's own calculation never matches the official grade.Answers
Frequently asked questions
What is a grade curve?
A grade curve is an adjustment applied to a set of scores after grading, usually because a test turned out harder than intended. Instead of changing anyone's answers, the teacher shifts the scores — adding points, scaling them, or remapping them — so the grades better reflect what the class actually learned.
How does the square-root curve work?
Take the square root of the score as a decimal, then read it back as a percentage — equivalently, curved = 10 × √(raw score). A 64 becomes 80, a 49 becomes 70, and a 100 stays 100. Low scores gain the most, which is why it's the most common curve in US schools.
What is a flat curve?
The simplest curve: the same number of points added to every score. If the highest raw score was 92 and the teacher adds 8, that student reaches 100 and everyone else rises by exactly 8 too. Rankings and gaps between students don't change at all.
What does "curved to the highest grade" mean?
The top score in the class is treated as 100 and every other score is scaled up by the same ratio. If the best result was 84, each score is multiplied by 100 ÷ 84 ≈ 1.19, so a 67 becomes about 79.8. That's the Top-score scale option in this calculator.
What is a bell curve for grades?
Strictly, grading on a bell curve assigns letters by rank — the top slice gets A's, the next slice B's, and so on, whatever the raw scores were. The gentler version, used here, shifts all scores so the class average lands on a target (often 75%, a C+/B− border). True rank-based curving can also lower grades; this calculator never curves anyone down unless you set a target below the current average.
Can a curve ever lower my grade?
With flat, percentage, square-root and top-score curves, no — every score stays the same or rises. Only strict rank-based bell curving can push a grade down, and a mean-shift curve will if the target average is set below the class's actual average. Check which method your teacher announced.
My teacher said the test is curved — how do I estimate my grade?
If you know the method, enter your score in the "just checking your own score" box with the same curve settings. For top-score and bell curves you'll also need the class's highest score or average — paste your best estimate of the class scores, or ask your teacher for those two numbers.
Should curved grades be capped at 100?
Most teachers cap at 100 so no one exceeds a perfect score, and this calculator does by default. Uncapping lets strong students keep the full benefit of the curve as a small bonus. Either is defensible — what matters is applying one rule to the whole class.
Is this calculator free?
Completely — no account, no install. Everything runs in your browser, so the scores you paste never leave your device. Teachers can paste a full roster's percentages without uploading student data anywhere.
Keep going
Related grade tools
Once the curve is set, these answer the next questions — what the curved grade does to a course average, a GPA, or the score needed on the final.
Grade Calculator
The main tool: scores plus syllabus weights in, your exact course grade, letter and GPA out.
Calculate →Final Grade Calculator
Find the exact score you need on your final exam to finish with the grade you want — or to just pass.
Calculate →GPA Calculator
Add every course with its credit hours and get your semester or cumulative GPA on the 4.0 scale.
Calculate →EZ Grader
For teachers: pick the number of questions and read off the grade for any number of wrong answers.
Open chart →