Mathematics & Statistics / Statistics
Z-Score Calculator
Formula
Z = (X - μ) / σ
Standard deviations from the mean
Standardize values against a distribution to measure how far an observation sits from the mean in standard deviations.
Formula
z = (x - mu) / sigma
Worked Example
valueX78
mean65
standardDeviation5
Result: z = 2.6A z-score of 2.6 means the observation is 2.6 standard deviations above the distribution mean.
Frequently Asked Questions
What z-score is considered unusual?
In many contexts, absolute z-scores above 2 are uncommon and above 3 are rare under normal assumptions.
Can z-score be negative?
Yes. Negative values indicate observations below the mean.