About the Grade Curve Calculator
This calculator applies two standard, widely used methods for curving exam or assignment scores: the linear (additive) curve and the square root curve. Both are common conventions taught in grading guides — enter a raw score, the class's highest score, and a target, and the tool shows the curved score, curved percentage, points added, and the resulting letter grade.
The linear (additive) curve
The linear curve is the simplest and most common method. First, find how many points the top scorer is short of the target (usually a perfect score):
Curve amount = Target top score − Highest raw score in class
That exact number of points is then added to every student's score:
Curved score = Raw score + Curve amount
Because every student receives the identical point boost, the gap between any two students — and therefore the class ranking — never changes. If the highest score already meets or exceeds the target, the curve amount is treated as zero rather than a negative adjustment, since a curve is not meant to lower anyone's grade.
The square root curve
The square root curve works differently: it converts each student's raw percentage into a curved percentage using the square root function:
Curved % = 100 × √(Raw % ÷ 100)
Because taking the square root of a fraction between 0 and 1 always produces a larger number, this method raises every score below 100%, and it raises lower scores by proportionally more than higher ones. A raw score of 100% still curves to 100%, and a raw score of 0% still curves to 0%, but a raw 64% jumps to 80% (since √0.64 = 0.8). Unlike the linear curve, the square root curve compresses the spread between students rather than preserving it.
How to use this calculator
- Enter your raw score and the maximum possible points for the assignment.
- For the linear method, also enter the highest score in the class and the target top score (typically equal to the maximum points, for a top score of 100%).
- For the square root method, only the raw score and maximum points matter — the highest-score and target fields are ignored.
- Choose a method from the curving method dropdown and press Calculate.
Choosing a method
Instructors typically choose the linear curve when they want to preserve the relative ranking and spacing between students exactly as it was, just shifted upward. They reach for the square root curve when the class did unevenly — some students far below average — because it narrows the gap by lifting the lowest scores the most. Neither method is universally "correct"; both are conventions, and the choice depends on the grading policy in place.