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Calculate z-score (standard score) from raw value, mean, and standard deviation. Supports p-value lookup.
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Calculates the z-score (standard score) from a raw value, population mean, and standard deviation. Also shows percentile rank and two-tailed p-value. Includes inverse lookup: enter a p-value to find the approximate critical z-value.
Z-scores standardize values from any normal distribution to the standard normal (μ=0, σ=1), enabling comparison across different scales. Essential for hypothesis testing, confidence intervals, and outlier detection.
This tool is part of the DevStackIO platform — a collection of free online developer tools from DevStackIO. Browse more free developer resources on DevStackIO.
Students, researchers, data analysts, quality engineers, and anyone performing statistical inference or standardization.
Enter the raw value (x), population mean (μ), and standard deviation (σ)
The tool computes z = (x - μ) / σ, percentile Φ(z)×100%, and two-tailed p-value
Or enter a two-tailed p-value (e.g., 0.05) to see the note about inverse CDF
85, 70, 101.962.58What does a z-score of 0 mean?
The value equals the mean.
What's the 95% confidence critical z?
±1.96 (two-tailed p = 0.05).
Can I use this for sample data?
Use t-distribution for small samples; z is asymptotically correct for large n.
Authoritative specifications, standards, and in-depth reading for Z-Score Calculator.
Z-Score
1.5
Percentile
93.319278%
Two-tailed p-value
13.361444%
Z = (x \u2212 \u03bc) / \u03c3. Percentile = \u03a6(z) \u00d7 100%. Two-tailed p = 2 \u00d7 (1 \u2212 \u03a6(|z|)) \u00d7 100%.
Uses standard normal CDF \u03a6(z) = \u00bd(1 + erf(z/\u221a2)). Runs locally.
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