Normal Distribution Calculator
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
100% FreeRuns in your browserBasic
Enter Values
Enter your values and press Calculate to see results.
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
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.