Z-Score Calculator
Compute z-score from value, mean, and standard deviation and optionally show percentile approximation.
Last reviewed by the Radiatus Cloud team
Output
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Find how unusual a value is
A z-score expresses how far a value sits from the mean, measured in standard deviations, which is how you compare values across different distributions. This calculator computes the z-score from a value, mean and standard deviation, and can show the corresponding percentile.
Why standardising is so useful
A raw value means little without context: is a score of 80 good? A z-score answers that by saying how many standard deviations above or below the mean it is, which places it on a universal scale regardless of the original units. That is what lets you compare a test score to a height, or convert a z-score into a percentile that says what fraction of the distribution falls below it. It is the foundation of much of statistics.
Context for any value
Everything runs in your browser, so nothing you enter is uploaded and the tool works without an account. That keeps your study material and notes private on your own machine while you learn.
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Frequently Asked Questions
What is a z-score?
A measure of how far a value is from the mean, in units of standard deviations. A z-score of 2 means the value is two standard deviations above the mean.
Why standardise a value?
Because a raw value has no context. A z-score places it on a universal scale, so you can compare values from completely different distributions.
What is the percentile?
The fraction of the distribution that falls below the value. The calculator can convert the z-score into this, saying how the value ranks.
When is a z-score used?
Throughout statistics, for comparing values, identifying outliers, and converting between raw scores and percentiles in a normal distribution.
Is my input uploaded?
No. The calculation runs entirely in your browser.
Privacy & Security
Calculated locally in your browser. No data is sent to any server.
How to Use
Enter x, mean, and standard deviation to compute z-score.
Disclaimer: This tool is provided "as is" without warranty of any kind. Results are for educational and utility purposes.