Z-score calculator
Express a value’s distance from the mean in standard deviations.
Formula
z = (value − mean) / standard deviation
Z-score ≈ ((85)-(70))÷(10)
How to use
- Enter the observed value.
- Enter the mean and positive standard deviation.
- Read the signed z-score.
Examples
- 85, mean 70, standard deviation 10: z=1.5.
- 60, mean 70, standard deviation 5: z=−2.
Frequently asked questions
What does z=−2 mean?
The value is two standard deviations below the mean.
Must the standard deviation be positive?
Yes. Zero would make the standardized distance undefined.
Is the z-score itself a probability?
No. A probability needs a distribution model; this tool returns only the standardized score.
Sources
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