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Z-score calculator

Compute the z-score of a value given the mean and standard deviation.

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Enter Value (x), Mean (μ), Standard deviation (σ) and the Z-score calculator works out Z-score straight away. For instance, with Value (x) = 85, Mean (μ) = 70 and Standard deviation (σ) = 10 it returns Z-score = 1.5.

How to use it

  1. Enter your values: Value (x), Mean (μ), Standard deviation (σ).
  2. Read the result instantly: Z-score.

Frequently asked questions

How does the Z-score calculator work?

It takes Value (x), Mean (μ) and Standard deviation (σ) and derives Z-score from them. The calculation is live as you type, so the result updates on every change.

Which values does the calculator ask for?

3 values: Value (x), Mean (μ) and Standard deviation (σ). Nothing else is required — no account, no file upload.

What does a typical calculation look like?

With Value (x) = 85, Mean (μ) = 70 and Standard deviation (σ) = 10, the calculator returns Z-score = 1.5. Those figures come from running this exact tool, so you can reproduce them by entering the same values.

What does it give for smaller values?

Scaled down to Value (x) = 43, Mean (μ) = 35 and Standard deviation (σ) = 5, Z-score comes out at 1.6. The relationship is worth checking at both ends before you rely on a single result.

When would I actually use this?

Summarising a dataset before drawing conclusions from it, checking whether a difference between two groups is real, and putting an interval around an estimate.

What is the most common mistake?

Reading a p-value as the probability that the hypothesis is wrong. It is the probability of seeing data at least this extreme if the null were true — a different statement, and a much weaker one.

What is the difference between the Z-score calculator and the Coefficient of variation calculator?

This one returns Z-score; the Coefficient of variation calculator returns Coefficient of variation and Mean. That is the whole difference — open the one whose figure you need.

Is there a tool for the next step?

Confidence interval calculator is the closest one after this: Compute a confidence interval for a mean from its standard deviation and sample size.

What else is worth having open alongside it?

Standard error calculator and Mean absolute deviation (MAD) calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from, and how current are they?

Distributions and test statistics are computed from their standard definitions, not from a lookup table, so results carry more digits than a printed table would. The assumptions each test makes are stated with it.

Further reading

All guides →
ExplainerWhat Is a Z-Score? Standard Deviations Above the MeanA z-score is z = (x − μ) / σ — how many standard deviations a value sits from the mean. Learn how to compute it, read the standard normal curve, and turn it into a percentile.ExplainerFibonacci and the Golden RatioThe Fibonacci sequence adds each pair of terms to make the next; the ratio of neighboring terms homes in on the golden ratio φ ≈ 1.618. See how, and where the pattern turns up.ExplainerMean, Median and Mode: What's the Difference?Mean, median and mode all describe the 'middle' of your data — but answer different questions. Here's what each means, with examples and when to use which.How-toHow to Calculate Standard Deviation (Step by Step)Standard deviation measures how spread out your data is. Here's the formula, a worked example, and the difference between population and sample.ExplainerWhat Is a Percentile? The 90th Percentile ExplainedA percentile tells you where a value ranks within a group. Learn what the 90th percentile really means and why a percentile is not the same as a percentage.How-toHow to Calculate a Weighted AverageA weighted average gives some values more influence than others. Learn the Σ(w·x) / Σw formula with grade and portfolio examples you can follow step by step.