Grading Bell Curve Calculator
Calculate the bell curve distribution of grades based on mean and standard deviation. Determine grade percentages and visualize the normal distribution.
Published by:
isCalculator Editorial Team
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How to use this tool?
This calculator estimates grade distribution based on a bell curve (normal distribution). Follow these steps:
- Enter Class Statistics – Input the Mean (μ) (average score) and Standard Deviation (σ) (spread of scores). Defaults are 75 and 10.
- Enter Your Score – Input the individual score you want to evaluate (default 85).
- Set Grade Thresholds – Define the minimum scores for grades A, B, C, and D. They must be in descending order (A > B > C > D). Scores below D receive an F.
- Click "Calculate" – The calculator computes:
- Z-Score: How many standard deviations your score is from the mean.
- Percentile Rank: The percentage of students scoring below your score.
- Grade Distribution: Estimated percentage of students earning each grade (A, B, C, D, F).
Note: All inputs must be numbers. Standard deviation must be greater than zero. Grade thresholds must strictly decrease (e.g., 90 > 80 > 70 > 60).
Previous Results
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Frequently Asked Questions
A grading bell curve is a normal distribution used to assign grades based on the mean and standard deviation of scores. It helps to standardize grades across different assessments.
The z-score indicates how many standard deviations a score is from the mean. A positive z-score means above average, negative means below average.
Yes, you can enter custom thresholds for A, B, C, and D grades. The calculator will estimate the percentage of students falling into each grade category.
