Z-Score Calculator
Calculate a z-score — how many standard deviations a value is from the mean.
A value's place in a distribution
A z-score measures how far a value sits from the mean of its data set, counted in standard deviations. This calculates it from a value, the mean and the standard deviation, giving a standardised measure of where a data point falls.
Enter the value, mean and standard deviation to find the z-score.
Why standardising is powerful
The z-score is useful because it puts any value on a common scale, stripping away the original units. A z-score of two means a value is two standard deviations above the mean, whether the data is heights, test scores or temperatures — which lets you compare positions across completely different data sets, like whether a score is more impressive on one test than another. For data that follows the familiar bell curve, z-scores also tie directly to probability: most values fall within a couple of standard deviations of the mean, so a large z-score marks a genuinely unusual value. Standardising to z-scores is one of the foundational moves in statistics, turning raw numbers into comparable positions.
Questions & answers
What does a z-score tell me?
How many standard deviations a value is from the mean — a z-score of two means two standard deviations above it, on a scale free of the original units.
Why is a z-score useful?
It lets you compare positions across different data sets, and for bell-curve data it ties to probability, so a large z-score marks an unusual value.
Is anything uploaded?
No. The calculation happens in your browser.