Z-score Calculator
Standardize a value relative to a supplied mean and positive standard deviation.
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How to use Z-score Calculator
The z-score is (observation − mean) ÷ standard deviation. Its sign indicates the side of the reference mean, and its magnitude counts standard deviations.
- Enter observation, reference mean, standard deviation.
- Check that the input follows the stated limits and uses consistent units.
- Run the calculator, review the result, then copy or download it.
Good to know
- Standard deviation must be positive. No normal-distribution percentile, diagnosis, significance claim, or population assumption is inferred.
- Decimal inputs have at most 120 characters and magnitude from 1e-100 to 1e15, or zero. Floating-point results are rounded to 12 significant digits; extreme derived results may underflow or be rejected. Exact integer results are identified separately.
Common questions
What calculation does Z-score Calculator perform?
The z-score is (observation − mean) ÷ standard deviation. Its sign indicates the side of the reference mean, and its magnitude counts standard deviations.
Does a z-score automatically give a probability?
No. A probability requires an appropriate distributional model in addition to a standardized distance.
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