About the Grade Curve Calculator
This grade curve calculator takes a list of raw test scores and applies the curving method your teacher or professor uses — adding a flat number of points, raising everyone so the top score becomes 100, scaling proportionally to the top score, the square-root curve, or a true bell curve that re-centres the class on a target average and spread. It shows the curved score and letter grade for every student and highlights your own result.
Teachers can use it to compare methods before posting grades, and students can use it to answer "what will my grade be after the curve?" once the class results are known. Paste scores separated by commas, spaces or new lines.
All scores are treated as percentages out of 100. Curved scores are capped at the maximum (100 by default) and never go below 0 unless you turn the cap off. Letter grades use the common US plus/minus scale (93+ = A, 90 = A−, 87 = B+ and so on).
With the default inputs, the your curved score is 84 %. Change any value above to recalculate instantly.
How to use the grade curve calculator
- 1Paste or type every score in the class, separated by commas or new lines.
- 2Enter your own raw score.
- 3Choose the curving method your instructor uses.
- 4Set the points to add, or the target mean and SD for a bell curve, if needed.
- 5Read your curved score and letter grade, then check the full table.
Formula and method
Flat and top-score curves add the same number of points to everyone; the top-score version chooses the points so that the highest score (H) becomes the maximum. Proportional scaling multiplies every score by Max ÷ H, which helps high scorers slightly more than low scorers. The square-root curve replaces each percentage with 10 × √x, so a 64 becomes 80 and an 81 becomes 90 — lower scores gain the most.
The bell curve converts each score to a z-score using the class mean (μ) and population standard deviation (σ), then maps it onto the target mean (μ′) and spread (σ′). Your rank in the class is preserved, but scores can go down as well as up. Every method is capped at the maximum and floored at zero unless the cap is turned off.
- x
- Raw score (%)
- y
- Curved score
- H
- Highest raw score in the class
- μ, σ
- Class mean and standard deviation
- μ′, σ′
- Target mean and standard deviation for the bell curve
Worked examples
Raise the top score (88) to 100
The best score is 88, so everyone gets 100 − 88 = 12 points. Your 72 (C−) becomes 84 (B), and the class average rises from 73.8 to 85.8.
Square-root curve on a 64
10 × √64 = 80, a 16-point boost. The top score of 88 only rises to 10 × √88 ≈ 93.81, while the lowest score of 58 jumps to about 76.16 — the square-root curve helps weaker scores most.
Bell curve to a 75 average, SD 10
The class mean is 73.8 with a population SD of about 8.83. Your 72 is about 0.20 SD below the mean, so it maps to 75 − 0.204 × 10 ≈ 72.96. The new class average is exactly the 75 target, with scores running from about 57.1 to 91.1.
Flat 5-point curve
Adding 5 points to every score moves your 72 to 77 (C+) and lifts the class average from 73.8 to 78.8.
Frequently asked questions
What does it mean to curve a grade?+
Curving adjusts raw scores after a test — usually upward — to account for a test that was harder than intended. Common methods add points, scale to the top score, apply a square root, or fit scores to a bell curve.
How does the square root curve work?+
Take the square root of your percentage and multiply by 10. A 49 becomes 70, a 64 becomes 80 and an 81 becomes 90. Low scores gain much more than high scores, and a 100 stays 100.
Can a bell curve lower my grade?+
Yes. A bell curve fits scores to a target average and spread, so if the class did better than the target, scores above and even near the mean can be pulled down. Most teachers only curve upward.
Which curve is the fairest?+
There is no single answer. Flat and top-score curves keep the gaps between students unchanged, proportional scaling rewards high scorers slightly more, and the square-root curve helps struggling students most. Bell curves rank students against each other.
Why is my curved score capped at 100?+
Most instructors do not award more than full marks, so the calculator caps curved scores at the maximum. Turn off the cap if your instructor allows extra credit above 100%.