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Z-Score Calculator
Enter a value, mean and standard deviation to get the z-score and its percentile.
Z-score
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Standard deviations from mean.
| Percentile | — |
|---|---|
| Above / below mean | — |
| Area to the left | — |
| — |
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How the Z-Score Calculator Works
A z-score tells you how many standard deviations a value sits from the mean: subtract the mean and divide by the standard deviation. A z of +1.5 means the value is one and a half standard deviations above average. Because it’s in standard units, you can compare values from completely different data sets.
If the data is roughly normal (a bell curve), the z-score also gives a percentile — the share of values below it — which this calculator estimates. A z of 0 is the 50th percentile; about 95% of values fall between z of −2 and +2.
z = (value − mean) ÷ standard deviation
Frequently Asked Questions
What is a z-score?
How far a value is from the mean, measured in standard deviations. Positive is above the mean, negative below.
How do I calculate a z-score?
Subtract the mean from the value and divide by the standard deviation. An 85 with mean 70 and SD 10 gives a z of 1.5.
What percentile does a z-score correspond to?
On a normal curve, a z of 0 is the 50th percentile, +1 is about the 84th, and +2 about the 97.7th. The calculator estimates it.
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