Z-Score and Percentile Calculator
Find a z-score and the percentile it corresponds to.
From z-score to probability
A z-score says how many standard deviations a value is from the mean, and for normally-distributed data it maps directly to a percentile — the portion of values below it. This calculates the z-score and its corresponding percentile together.
Enter your value, mean and standard deviation to see the z-score and percentile.
Tying the z-score to the bell curve
The reason a z-score is so powerful is its link to the normal distribution, the familiar bell curve that describes so much natural data. For bell-curve data, a given z-score always corresponds to the same percentile, regardless of the original units — a z-score of zero sits at the 50th percentile (the mean), and the well-known rule that most values fall within a couple of standard deviations of the mean is really a statement about z-scores and percentiles. This is what turns a z-score from an abstract distance into a concrete probability: it tells you not just how far a value is from the average, but how it ranks, and how unusual it is. That translation from position to percentile is one of the workhorses of applied statistics.
Z-Score and Percentile Calculator FAQ
How does a z-score relate to a percentile?
For normally-distributed data, a z-score maps directly to the portion of values below it — a z-score of zero is the 50th percentile, at the mean.
What does this add over a plain z-score?
It converts the z-score into a percentile, telling you not just the distance from the mean but the rank and how unusual the value is.
Is anything uploaded?
No. The calculation happens in your browser.