Z-Score Calculator
Convert a value into a z-score and find its percentile and the probability of scoring above it.
How to use it
- Enter the value The data point you want to standardize.
- Enter the mean and standard deviation For the distribution it comes from.
- Read the z-score See the z-score, percentile and upper-tail probability.
Examples
| x=130, μ=100, σ=15 | z = 2.0 |
|---|---|
| z = 2.0 | ~97.7th pct |
About this tool
A z-score, or standard score, tells you where a value sits relative to the average, measured in standard deviations. It makes it possible to compare values from different scales — like test scores from two different exams.
This calculator turns a value into a z-score, then reports its percentile and the probability of a higher value, using the standard normal distribution. Everything runs in your browser.
Frequently asked questions
What is a z-score?
A z-score is how many standard deviations a value is above (positive) or below (negative) the mean. A z of 0 is exactly average.
How is the percentile found?
From the standard normal distribution. For example, a z-score of 1.96 is at about the 97.5th percentile.
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Updated June 12, 2026