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
Sample SD
5.2372
Population SD
4.8990
Sample variance
27.4286
Mean
18.0000
Psst — share this and help Rex grow
One click, a permanent link with your numbers baked in.
How to use this
- 1Enter numbers.
- 2Read your sample sd on the right — it updates as you type.
- 3Hit Share to keep the scenario or send it to someone.
About this calculator
Computes mean, variance, and standard deviation (both sample and population) from a number list.
Worked example
Using the values the calculator loads with:
Inputs
- Numbers: 10, 12, 23, 23, 16, 23, 21, 16
Results
- Sample SD: 5.2372
- Population SD: 4.899
- Sample variance: 27.4286
- Mean: 18
What each field means
Inputs
- Numbers
- Free text used in the calculation. Defaults to "10, 12, 23, 23, 16, 23, 21, 16".
Results
- Sample SD
- 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.
- Population SD
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Sample variance
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
- Mean
- Returned as a decimal number. It recalculates instantly whenever you change an input, so you can compare scenarios without reloading.
FAQ
How does the standard deviation calculator work?
Computes mean, variance, and standard deviation (both sample and population) from a number list.
What do I need to enter?
Just one value: numbers. Each field starts with a sensible default, so you can change one number at a time and watch the result move.
What does the sample sd 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). Standard Deviation Calculator. Retrieved from https://www.revenuelab.fyi/toolbox/standard-deviation
<p>Source: <a href="https://www.revenuelab.fyi/toolbox/standard-deviation" target="_blank" rel="noopener">Standard Deviation Calculator — RevenueLab</a> (2026).</p>
Source: [Standard Deviation Calculator — RevenueLab](https://www.revenuelab.fyi/toolbox/standard-deviation) (2026).