Z-Score Calculator
Calculate a z-score and percentile from value, mean and SD.
About this tool
A z-score measures how many standard deviations a value is from the mean of its distribution. This also converts the z-score into a percentile, assuming a normal (bell-curve) distribution — showing roughly what percentage of values fall below it.
Key Features
- Z-score from value, mean and standard deviation
- Percentile (assuming a normal distribution)
- Works with any units — test scores, measurements, etc.
How to Use
- Enter the value you want to evaluate.
- Enter the distribution's mean.
- Enter the distribution's standard deviation.
- Click Calculate Z-Score.
Benefits
- Understand how unusual or typical a value is
- Compare values from different distributions on a common scale
- Interpret standardized test scores
Frequently Asked Questions
It means the value is exactly equal to the mean — neither above nor below average within the distribution.
Yes — the percentile conversion assumes a normal (bell-curve) distribution. The z-score itself is valid for any distribution, but the percentile figure is only accurate if your data is roughly normally distributed.