SHAPES, DATA, AND SCHOOL MATH
Z-Score Calculator
Calculate a z-score from an observed value, mean, and standard deviation with the difference shown.
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Enter your values and select Calculate. Your result stays on this device.
How it works
z = (observed value − mean) ÷ standard deviation.
Assumptions
The entered mean and standard deviation describe the comparison distribution; this tool does not calculate probability or prove normality.
About this calculator
Use this z-score calculator to answer how many standard deviations a value is above or below an entered mean. The signed difference remains visible for a quick reasonableness check.
How to use it
- Enter the observed value.
- Enter the comparison mean.
- Enter a positive standard deviation.
- Calculate and interpret positive results as above the mean and negative results as below it.
Use case
z score calculator: a clear planning check
Calculate z = (value − mean) ÷ standard deviation and keep the signed difference and comparison inputs visible.
Express an observed value as a signed number of standard deviations from an entered mean.
Method and update
Last reviewed: 2026-08-22. This tool performs the stated formula locally in your browser using the values you enter.
Frequently asked questions
What does a z-score of 1 mean?
The observed value is one standard deviation above the mean.
Can a z-score be negative?
Yes. A negative z-score means the value is below the mean.
Does a z-score give a percentile automatically?
No. Converting a z-score to a percentile requires a distribution assumption and lookup or probability calculation.
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