Rex says
The fast lane for the math you almost remember from school. Type the numbers, get the answer, move on with your day.
Try a scenario
Click to load — tweak from there.Inputs
Result
Z-score
2.0000
Percentile
97.72%
Share above your value
2.28%
Two-tailed p-value
4.550%
Read
Within the typical range
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter your value (x).
- 2Enter mean (μ).
- 3Enter standard deviation (σ).
- 4Read your z-score on the right — it updates as you type.
- 5Hit Share to keep the scenario or send it to someone.
About this calculator
A z-score says how many standard deviations a value sits from the mean. Converting it to a percentile tells you what share of the distribution falls below your value.
Worked example
Using the values the calculator loads with:
Inputs
- Your value (x): 130
- Mean (μ): 100
- Standard deviation (σ): 15
Results
- Z-score: 2
- Percentile: 97.72%
- Share above your value: 2.28%
- Two-tailed p-value: 4.550%
- Read: Within the typical range
What each field means
Inputs
- Your value (x)
- The your value (x) used in the calculation. Starts at 130 so you have a working example on load.
- Mean (μ)
- The mean (μ) used in the calculation. Starts at 100 so you have a working example on load.
- Standard deviation (σ)
- The standard deviation (σ) used in the calculation. Starts at 15 so you have a working example on load.
Results
- Z-score
- Returned as a decimal number and shown as the headline result. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Percentile
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Share above your value
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Two-tailed p-value
- Returned as a percentage. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Read
- Returned as a plain value. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the z-score calculator work?
A z-score says how many standard deviations a value sits from the mean. Converting it to a percentile tells you what share of the distribution falls below your value. The underlying maths is: z = (x − μ) ÷ σ. Percentile comes from the normal cumulative distribution.
What do I need to enter?
3 values: your value (x), mean (μ), and standard deviation (σ). Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the z-score result mean?
It is returned as a decimal number and updates live as you edit the inputs, so you can compare two or three versions of a scenario in a few seconds.
Is this calculator free, and do I need an account?
Yes, it's free, and no account is required. Nothing you type is stored on our servers — the maths runs entirely in your browser.
How accurate is the result?
It applies the standard formula exactly, so the arithmetic is precise. Results are rounded for display; the underlying calculation keeps full precision.
Who is this tool for?
It's built for students, developers, and anyone who needs the answer right now without setting up a spreadsheet.
Accuracy and limitations
- Results are rounded for display; the underlying calculation keeps full precision.
- Very large or very small inputs may hit floating-point limits in the browser.
- Inputs outside the accepted range are clamped rather than rejected.
Related tools
Cite this calculator
Writing about this topic? Grab a citation — every link helps keep these tools free.
RevenueLab. (2026). Z-Score Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/z-score
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/z-score" target="_blank" rel="noopener">Z-Score Calculator — RevenueLab</a> (2026).</p>
Source: [Z-Score Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/z-score) (2026).