Grade Curve Calculator — How Grading on a Curve Works

Formula

How this is calculated

Grade curving adjusts scores after an exam when the class average or score distribution is lower than the instructor intended. The four most common methods are: (1) Square root curve — multiplies the square root of the raw score by 10, so a 64 becomes 80. This boosts low scores the most and is self-limiting at 100 for a perfect paper. (2) Flat addition — simply adds a fixed number of points to every score and caps at 100. Straightforward and transparent, but it does not compress the spread of scores. (3) Scale to highest — divides each score by the class top score and multiplies by 100, effectively making the highest score a 100. A class where the best student scored 85 would see all scores scaled up by 100/85 ≈ 1.18. (4) Mean shift — adds the difference between the target mean and the actual class mean to every score. If the class averaged 62 and the instructor wants a 75 average, everyone gets +13 points (capped at 100).

The XY plot visualises the transformation function: the x-axis is any possible raw score (0–100) and the y-axis is the resulting curved score. The dashed diagonal would be no curve at all (curved = raw); curving functions bow above it. Your own position on the curve is marked with a red dot. For the square root curve the function is concave, giving the greatest boost to students who scored the lowest — a 36 becomes a 60, but an 81 only becomes a 90. For linear methods (flat addition, mean shift) the line is parallel to the diagonal but shifted upward.