Z-Score Calculator

The raw score you want to standardise — e.g. one student’s test result of 75.

The mean of the population or distribution the value comes from — e.g. the class average on the same test.

The standard deviation of the same population. The z-score counts how many of these units the value lies above or below the mean.

A standardised score: 0 is exactly average, positive values lie above the mean, negative below. The tool returns its percentile and tail areas.

The percentile to convert, from 0 to 100. Example: 97.5 returns z = 1.96, the value that 97.5% of the distribution falls below.

The smaller of the two z-scores bounding the interval. Use negative values for points below the mean, e.g. -1.

The larger z-score of the interval. With z₁ = −1 and z₂ = 1 the area between is about 68%, matching the empirical rule.