What is the Z-Score Calculator?
Calculate the z-score of a value and its percentile under a normal distribution. Paste a list of numbers from any spreadsheet or document and get descriptive statistics instantly. Each statistics calculator also charts your data so outliers stand out.
How to use the Z-Score Calculator
- Enter your value, your mean, your standard deviation.
- Results update automatically as you type; you can also press Calculate.
- Read the output: z-score, percentile (below x).
- Use the 📊 chart to see the result visually, then copy or share it.
Formula and method
Worked example
With value = 85, mean = 70, standard deviation = 10, the Z-Score Calculator returns z-score: 1.5000; percentile (below x): 93.32%.
Tips for better results
- Use sample standard deviation (n − 1) for samples and population (n) for complete data sets.
- Check the chart for outliers before trusting a mean.
- Quartiles here use the inclusive interpolation method, matching Excel’s QUARTILE.INC.
Frequently asked questions
What does the Z-Score Calculator do?
Calculate the z-score of a value and its percentile under a normal distribution.
How is it calculated?
The Z-Score Calculator uses this method: z = (x − μ) ÷ σ.
Can you show an example?
With value = 85, mean = 70, standard deviation = 10, the Z-Score Calculator returns z-score: 1.5000; percentile (below x): 93.32%.
Is the Z-Score Calculator accurate?
Yes. It uses standard formulas and exact constants, and the results are verified by our automated test suite. Values are displayed to up to 12 significant digits.
Is this tool free and private?
Yes — the Z-Score Calculator is completely free with no sign-up, and it runs entirely in your browser, so the values you enter are never uploaded to our servers.
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