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Get NordVPN →Z-Score Calculator – Standard Score
Enter a value, the mean, and the standard deviation to get the z-score. Runs in your browser — no signup.
Enter value, mean, and standard deviation.
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How it works
What is a z-score?
A z-score, or standard score, tells you how many standard deviations a value is from the mean. It is calculated as z = (x − μ) / σ, where x is the value, μ is the mean, and σ is the standard deviation. A z-score of 0 equals the mean; +1 is one standard deviation above it.
Interpreting the result
Positive z-scores are above the mean, negative ones below. In a normal distribution, about 68% of values fall within ±1, 95% within ±2, and 99.7% within ±3. Z-scores let you compare values from different datasets on the same scale.
Frequently asked questions
›What is the z-score formula?
z = (x − μ) / σ — the value minus the mean, divided by the standard deviation.
›What does a negative z-score mean?
The value is below the mean. A z-score of −1.5 is 1.5 standard deviations below average.
›What is a good or unusual z-score?
Values beyond ±2 or ±3 are uncommon in a normal distribution and are often treated as outliers.
›Can the standard deviation be zero?
No. Dividing by zero is undefined, so the SD must be greater than zero.
›Is the z-score the same as a percentile?
Related but not identical. A z-score maps to a percentile via the normal distribution's cumulative function.
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