How are the curved cutoffs calculated?

The tool computes the class mean and standard deviation, then places letter-grade boundaries at fixed multiples of the SD around the mean. By default the mean sits at the C band, with each higher grade one half standard deviation above and lower grades below, so grades reflect relative standing.

What is standard deviation here?

Standard deviation measures how spread out the scores are. A small SD means most students scored close to the mean, so grade bands are narrow; a large SD means scores are widely spread, producing wider bands. The tool uses the population standard deviation of the entered scores.

Should I always grade on a curve?

No. Curving is appropriate when an exam was unusually hard or you want grades to reflect relative rank. For mastery-based courses, absolute cutoffs (90=A, 80=B) are fairer. Use this tool when relative standing is what you want to reward.

Why does the mean map to C by default?

Mapping the mean to C produces a roughly symmetric distribution where the average student earns an average grade. You can shift the center to B- for a more generous curve; that raises every cutoff and moves more students into higher bands.

Does the calculator handle duplicate or zero scores?

Yes. Every numeric value you enter is counted, including zeros and repeats. Non-numeric tokens are ignored. The mean and SD reflect all valid scores, so leave out entries you do not want to influence the curve.

Exam Grade Distribution Calculator

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Exam grade distribution calculator

Grading on a curve assigns letters by relative standing instead of fixed percentages. This tool takes a list of raw scores, computes the mean and standard deviation, and places A-F cutoffs at standard-deviation intervals around the mean — then counts how many students fall into each band so you can see the shape of the distribution before you commit.

How it works

The calculator first computes the mean (average) and the population standard deviation (spread) of your scores. It then sets letter boundaries relative to the mean. With the default center at C, the bands are:

A   : mean + 1.5 SD and above
B   : mean + 0.5 SD  to  mean + 1.5 SD
C   : mean − 0.5 SD  to  mean + 0.5 SD
D   : mean − 1.5 SD  to  mean − 0.5 SD
F   : below mean − 1.5 SD

Shifting the center to B- lifts every cutoff by one band, producing a more generous curve. Each student is then counted into the band their score falls in.

Tips and notes

A curve is most defensible when an exam was harder or easier than intended, because it ties grades to relative performance. Watch the standard deviation: a very small SD compresses the bands so a few points separate an A from a C, while a large SD spreads them out. For mastery-based courses, absolute cutoffs are usually fairer than a curve.