Grade Curve Calculator

Apply a curve to a set of class scores and compare the methods.

Please note: Grading rules vary by institution, and many schools round, cap or weight differently. Always confirm against your own syllabus or registrar before relying on a result.

What the Grade Curve Calculator does

Curving adjusts a set of raw scores upward, usually because an assessment proved harder than intended. The method matters: some curves preserve the gaps between students, others deliberately compress them to help those at the bottom more.

Formula

Scale to top: Curved = Raw × 100 ÷ Highest
Square root: Curved = √Raw × 10
Flat: Curved = Raw + Points
Target mean: Curved = Raw + (Target mean − Actual mean)

Inputs explained

Input	Unit	Required	Notes
Class scores	text	Yes	Every student’s raw percentage.
Curve method	one of 4 options	Yes	—
Points to add	number	In some modes	Shown Curve method is Add a flat number of points.
Target class mean	%	In some modes	Shown Curve method is Shift to a target class mean.
Cap scores at 100	yes / no	Optional	—
Grade scale	one of 3 options	Yes	Check your syllabus — schools differ on whether an A+ is worth more than an A.

How to use it

Choose Curve method and Cap scores at 100.
Enter Class scores.
Fill in the remaining inputs the form shows for your choice.
Select Calculate.

Worked example

Class scores of 45, 62, 71, 58 and 83, scaling the top score to 100.

Scores: 45, 62, 71, 58, 83
Method: Scale top to 100

The factor is 100 ÷ 83 = 1.2048, giving 54.22, 74.70, 85.54, 69.88 and 100. The mean rises from 63.8% to 76.87%.

Reading the result

The "how the methods compare" table lets this specific class's score distribution be checked against every method at once, rather than reasoning about curve methods in the abstract.
"Largest individual gain" flags whichever student benefits most from the chosen method — worth checking against "passing at 60% after" to see whether the curve rescued a specific student or shifted everyone uniformly.

Assumptions and limitations

Fixed-formula methods like square-root and scale-to-top apply identically regardless of class size — a curve appropriate for a large distribution can behave oddly on a very small sample where one outlier score dominates the highest or mean.
Capping at 100 can compress the top of a flat-addition curve disproportionately, pushing multiple already-high scorers to an identical ceiling and losing their original ranking.

Common mistakes

Assuming the square-root curve is always the most generous method — the notes and FAQ explain it lifts low scores most and high scores least, so for a class already doing well, scale-to-top or a flat addition may raise the mean more.

Frequently asked questions

Which curve method is fairest?

It depends on intent. Scaling to the top preserves relative performance; the square root curve helps struggling students disproportionately; a flat addition treats everyone identically in absolute terms.

Why is the square root curve so common?

Because it lifts failing scores substantially while barely moving high ones, which rescues a badly written exam without devaluing top performance.