Z-Score Calculator
Enter a value, the mean and the standard deviation to see how unusual the value is.
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What a z-score is
A z-score says how many standard deviations a value is above or below the mean: z = (x − μ) ÷ σ. A mark of 82 in a test with mean 70 and standard deviation 8 has z = 1.5, which is better than about 93% of students if the marks are normally distributed.
Reading the result
- z = 0 is exactly average. About 68% of values fall between −1 and 1, and about 95% between −2 and 2.
- The percentile is the share of values below yours, from the standard normal distribution.
- The two-tailed p-value is the chance of a value at least this far from the mean in either direction, used in hypothesis tests (below 0.05 is often called significant).
Z-scores let you compare results on different scales, for example a maths mark and a physics mark. Percentiles assume the data roughly follows a normal (bell-shaped) curve, so with very skewed data, treat them as an approximation.
Free to useNo software to install — works in any modern browser.
No signup neededOpen the tool and start straight away.
Runs in your browserNothing you enter is sent to a server.
Works on mobileSame tool on your phone, tablet or desktop.
How it works
- Enter — type or paste your values or text.
- Get the result — it is worked out in your browser.
- Adjust — change the inputs to compare, or copy the result.
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