Free Online Tool
Grading on a Curve Calculator
Three curve methods: linear scale, square root curve, and bell curve (z-score). Get your curved percentage and letter grade instantly. Free, no install, no signup.
Curve Settings
E.g. max raw was 88/100 → set to 100 to shift everyone up proportionally
Curved Score
72%
C−No change — score already at target
Before vs. After
Raw Score
72%
C−Curved Score
72%
C−Standard Grade Scale
Related Calculators
Which Curve Method Helps You the Most?
It depends on your raw score relative to the class average:
Example: Raw score 60/100
The square root curve is uniquely generous to very low scores. A 36/100 raw → 60%, gaining 24 points. The same linear curve (max 80 → 100) would only give 45%. If you scored below 60% raw, square root is almost always best.
The Bell Curve Fairness Debate: What Professors Don't Say
Bell curve grading sounds scientific but has a dirty secret: it creates a forced ranking. If the target grade distribution is predetermined (e.g., 30% A, 40% B, 20% C, 10% D/F), then no matter how well the class performs, roughly 10% will always fail.
This is common in competitive graduate programs and law schools. Contrast with criterion-referenced grading where everyone who scores ≥ 90 gets an A, regardless of how many that is.
Our bell curve method is the pure z-score shift — it moves the mean without forcing a distribution. It does NOT create a forced rank order.
Frequently Asked Questions
What is grading on a curve?
Grading on a curve adjusts raw scores upward to compensate for an unusually difficult exam. The three most common methods are: (1) Linear scale — proportionally rescale all scores so the highest score becomes 100%. (2) Square root curve — multiply √(raw/max) × 100, which helps low scores more than high scores. (3) Bell curve — shift the class mean and standard deviation to match target values, preserving relative ranking.
What is the square root curve grading method?
The square root curve formula is: curved score = √(raw score / max score) × 100. A 64/100 raw score becomes √(0.64) × 100 = 80. A 49/100 becomes √(0.49) × 100 = 70. This method disproportionately helps students with lower scores — a 36 becomes 60, gaining 24 points, while a 81 becomes 90, gaining only 9 points.
When should a teacher use a bell curve vs. linear curve?
Use a linear scale when the exam was uniformly harder than expected. Use a bell curve when scores are distributed oddly — if a few students aced it and most scored 50–65. Bell curve maintains relative differences while shifting the distribution. Linear curves treat everyone equally; bell curves preserve class rank.
Does grading on a curve always raise grades?
Not necessarily. A true bell curve can lower grades for students who scored above the class mean if the target mean is lower than the actual mean. In practice, most professors set a minimum so that no individual score decreases.
What is the formula for grading on a curve with linear scaling?
Linear scaling formula: curved score = (raw score / max raw score) × target max. If the highest score in the class was 88/100 and you scale to 100: every score is multiplied by (100/88). A score of 72 becomes 72 × (100/88) = 81.8%.
Note
This calculator is for educational purposes. Always check with your instructor for the specific curve method they are applying.