Grade Curve Calculator
Apply a curve to a class of test scores: flat boost, square-root, or top-score-to-100.
Compares raw scores and curved scores side by side.
A grade curve is a transformation applied to raw test scores when the original scores were too low (or too high) to reflect what the instructor was trying to measure. The three curves below cover almost every situation a teacher actually runs into.
The flat curve is the simplest. Add a fixed number of points to every score. If the test was poorly written or had a question with no correct answer, this is the honest fix. The downside is that it does not change the spread; a 30 stays 30 points behind a 60 even after both gain 10 points.
The square-root curve is the classic. Take each score out of 100, take its square root, and multiply by 10. Algebraically:
curved = 10 × √raw
A 49 becomes 70, a 64 becomes 80, an 81 becomes 90, and a 100 stays 100. It compresses the scale and rewards weaker students more than stronger ones, which is exactly what a teacher wants when the median came in lower than expected and a few students nailed it. This is the curve most American high schools and colleges mean when they say “the test was curved.”
The top-score curve normalises the highest raw score to 100 and pulls everyone else along proportionally:
curved = raw × 100 / max(raw)
So if the highest score on a test was 87, every score gets multiplied by 100/87 ≈ 1.149. The student who got the 87 now has 100, the student who got 80 has about 92, and so on. This curve is popular in graduate-school grading where the assumption is that the best work in the room defines what an A looks like.
Each curve serves a different purpose, and choosing the right one is its own skill. If you are a teacher trying to decide, ask yourself this: was the test too hard for everyone equally, or did most students miss a specific concept that you forgot to cover? A flat boost answers the first question; a square-root answers the second. The top-score curve is closer to a redefinition of the grading rubric than a curve, and it is the most controversial of the three with students and parents.
The calculator accepts any list of scores, applies all three curves, and shows them side by side. It also reports the new mean, median, and the change in the lowest passing grade, which is the number administrators usually ask about first.