Z-Score Calculator

A Z-score of 1.96 corresponds to the 97.5th percentile of a standard normal distribution and is the critical value for a 95% confidence interval — 95% of values fall within ±1.96 standard deviations of the mean.

A negative Z-score means the value is below the mean. A Z-score of -1 means the value is 1 standard deviation below average. About 16% of values in a normal distribution fall below a Z-score of -1.

Z-scores are used when the population standard deviation is known and sample size is large. T-scores are used when the standard deviation is unknown and must be estimated from the sample — the more common scenario with small samples.