Z Score Calculator
Calculate a dimensionless standard score from an observation, population mean and standard deviation.
A QUICK WALKTHROUGH
How to use this tool
- Enter the observation, population mean and standard deviation.
- Convert all values to the same unit and use matching unit labels.
- Calculate the standard score.
Formula and units
z = (X − μ) / σ. Enter finite numbers; σ must be strictly positive. Use the same units for all three values and enter matching unit labels after any conversion.
Interpretation
A z score gives the signed distance from the mean in standard deviations. It is not a percentile or probability; those require a distribution assumption. This tool uses supplied population statistics and does not estimate them from a data list.
Privacy
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GOOD TO KNOW
Common questions
Is a z score a percentile?
No. A z score measures distance in standard deviations. A percentile requires a distribution model or an empirical data set.