Z-Score Calculator
Convert any raw score to a z-score and percentile: see how many standard deviations it is from the mean
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Common Z-Score Reference
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Assumes an approximately normal distribution
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Each row recalculates with your current inputs. Tap a row to apply it.
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Enter score, mean, and deviation
Fill in your raw score, the mean, and the standard deviation above
Z-Score Calculator FAQ
What is a z-score?
A z-score (standard score) tells you how many standard deviations a raw score is away from the population mean. z = (x − μ) ÷ σ. A z of +1.5 means the score is 1.5 standard deviations above the mean; a negative z means below the mean.
How do I turn a z-score into a percentile?
The percentile is the area under the standard normal curve to the left of z, written Φ(z). For example Φ(1.5) ≈ 0.9332, so z = 1.5 is roughly the 93rd percentile. This calculator computes Φ(z) automatically.
What do I use for μ and σ?
Use the mean and standard deviation of the reference group you are comparing against — for example the class average and its standard deviation on an exam. If only a sample is available, the sample mean and sample standard deviation are commonly used as estimates.
Can a z-score be greater than 3 or less than −3?
Yes. Z-scores have no fixed bounds; ±3 just covers about 99.7% of a normal distribution. Very large |z| means the value is extreme relative to the reference group, or that the distribution is not close to normal.
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