Grade Curve Calculator
When raw test scores come out lower than expected, instructors often apply a curve to adjust them upward. The three most common methods are a flat curve that adds the same points to everyone, a top-score curve that scales the highest mark up to 100 and everyone else proportionally, and a square-root curve that gives a bigger boost to lower scores. This calculator takes your raw percentage score, the highest score in the class, and a flat-points value, then shows what each curve would produce, all capped sensibly at 100. It is a transparency tool: it computes each method exactly so you can see the effect, not a judgment of which curve is appropriate.
Curve formulas
flat curve = min(raw + flat points, 100)
top-score curve = min(raw / top score * 100, 100)
square-root curve = min(10 * sqrt(raw), 100)
best gain = max(of the three) - raw
The square-root curve assumes a percentage score out of 100, so 10 times the square root maps 0 to 0 and 100 to 100 while lifting the middle. All curves are capped at 100.
Notes on curving
- A flat curve preserves the gap between students; everyone moves up equally.
- A top-score curve assumes the highest mark represents an achievable ceiling.
- A square-root curve compresses the scale, helping lower scorers most.
- Some institutions cap curved grades at 100; this calculator does the same.
- The chosen method is set by the instructor and the course grading policy, not by this tool.
Grade curves: frequently asked questions
What is a grade curve?
A grade curve is an adjustment a teacher applies to raw scores, usually to raise them. Common methods are a flat curve that adds a fixed number of points to everyone, a top-score curve that scales scores so the highest mark becomes 100, and a square-root curve that boosts lower scores more than higher ones. This calculator computes all three from your raw score.
How does a flat curve work?
A flat curve adds the same number of points to every score. If you scored 72 and the instructor adds a flat 8 points, your curved score is 80. The calculator caps the flat-curved result at 100 since most grading does not exceed full marks.
How does a top-score (linear) curve work?
A top-score curve divides each raw score by the highest score in the class and multiplies by 100, so the top scorer gets 100 and everyone else scales proportionally. If the top score is 90 and you scored 72, your curved score is 72 / 90 * 100, which is 80.
How does a square-root curve work?
A square-root curve replaces a percentage score with 10 times its square root (for a score out of 100). A 64 becomes 10 times the square root of 64, which is 80. Low scores rise more than high scores, and a perfect 100 stays 100. It is a common gentle curve.
Which curve should my instructor use?
That is entirely up to the instructor and the grading policy. This calculator shows what each common method would produce so you can understand the effect. It does not decide which curve is fair or correct for a given class.
Official sources
- U.S. Department of Education: official site (grading context).
- National Center for Education Statistics: NCES (education data).
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. The curve formulas are standard arithmetic. See our methodology.