Normal Distribution Calculator
Find probabilities, percentiles and areas under the curve for any normal distribution using this free calculator that runs in your browser.
Enter Values
How to use this calculator
- Enter the mean, standard deviation and a value x.
- Read the probability below and above x.
How it works
Converts x to a z-score, then uses the normal cumulative distribution (error-function approximation) for P(X<x).
Worked example
μ=100, σ=15, x=130. ≈ 97.7% below, 2.3% above.
Tips
- Runs entirely in your browser. Your inputs are not saved or transmitted.
Frequently asked questions
How accurate is it?
The error-function approximation is accurate to a few decimal places — fine for coursework.
Privacy?
Runs entirely in your browser. Your inputs are not saved or transmitted.
Related tools
- Z-Score Calculator
- Average (Mean) Calculator
- Binomial Probability Calculator
- Conditional Probability Calculator
- Margin of Error Calculator
- Probability Calculator
Explore more in Maths, Education & Science.
Cite this tool
Zerdly. (2026). Normal Distribution Calculator. Retrieved from https://www.zerdly.com/tools/normal-distribution-calculator/
Tip: Enter any known values to calculate the remaining results.
Designed to run locally in your browser. Tool inputs are not intentionally stored by Zerdly unless stated otherwise.