Use the free Z Score Calculator on AixKit to get instant, accurate results in your browser. No sign-up or installation required.
See how many standard deviations a value sits from the mean — instantly.
A z-score tells you how far a value is from the mean of a dataset, measured in standard deviations. This calculator uses the formula z = (x − μ) / σ to return that number directly.
The formula is z = (x − μ) / σ, where x is your value, μ is the population mean, and σ is the standard deviation. A z of 0 means the value equals the mean; positive z is above the mean, negative z is below. In a normal distribution, about 68% of values fall within ±1, 95% within ±2, and 99.7% within ±3.
It is the number of standard deviations a value sits above or below the mean of a distribution. It standardises raw scores so they can be compared across different scales.
It means the value is below the mean. A z-score of −1.5 sits one and a half standard deviations below average.
By convention, |z| greater than 2 is uncommon and |z| greater than 3 is rare in a normal distribution. Outlier cut-offs are usually set around ±2 or ±3.
Use a z-score when you know the true population mean and standard deviation, or your sample is large. Use a t-score for small samples where you only have sample statistics.
You can compute z, but its interpretation in terms of percentiles only holds when the data is approximately normal. For skewed data, use percentile ranks instead.
