A z-score is the number of standard deviations a value lies from the mean. It is calculated as (value minus mean) divided by the standard deviation, so a z-score of 2 means the value is two standard deviations above average.

How do you read a z-score as a percentile?

The standard normal distribution maps each z-score to a cumulative probability. This tool reports the percentage of the distribution below your value, which is the percentile under a normal-distribution assumption.

Is my data uploaded anywhere?

No. Every calculation runs locally in your browser and nothing is sent to a server.

Z-Score Calculator

Convert a value to a standard score — and back.

Z-score calculator

A z-score (or standard score) tells you how many standard deviations a value sits above or below the mean: z = (x − μ) / σ. This calculator converts a raw value to a z-score and reports the percentile below it, or converts a z-score back to its raw value.

Everything runs in your browser — your numbers never leave your device.