Free online Z-score calculator. Enter a value, mean, and standard deviation to compute the Z-score. Supports normal distribution probability lookup. Pure frontend, no data upload.
A Z-score (standard score) indicates how many standard deviations a data point is from the mean. Formula: Z = (X - μ) / σ, where X is the value, μ is the mean, and σ is the standard deviation. Positive Z means above mean, negative means below.
Z-scores are used for data standardization, comparing data on different scales, identifying outliers, and calculating normal distribution probabilities. Examples: comparing test scores across subjects, detecting anomalies, assessing investment risk.
Z=0 means at the mean; Z=1 means 1 standard deviation above (about 84.13 percentile); Z=-1 means 1 below (about 15.87 percentile); |Z|>2 is typically considered an outlier.
Yes. The tool uses the error function (erf) approximation to calculate cumulative normal distribution probabilities, giving P(X
No. All calculations happen locally in your browser. Data is never uploaded to any server.