Standard Deviation Calculator
Variance, standard deviation and the rest of the summary.
Standard Deviation Calculator computes population and sample standard deviation, variance, mean, standard error, quartiles and the interquartile range from a list of numbers, and shows the deviation of each value from the mean. It explains which of the two divisors applies, and the list never leaves your browser.
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Runs entirely on your device. No file or text you enter here is uploaded. How to verify it.
How to use Standard Deviation Calculator
- Paste your numbers.
- Choose sample or population, or read both.
- Read the deviation, variance, quartiles and the per-value table.
Questions about Standard Deviation Calculator
Sample or population — which do I need?
If your numbers are the entire group you care about, use population (divide by n). If they are a sample you are using to estimate a larger group, use sample (divide by n−1). Almost all real analysis is the sample case; the n−1 correction exists because a sample underestimates the spread of its parent population.
What do the quartiles tell me?
Q1 and Q3 mark the middle half of the data, and their gap is the interquartile range. It is a robust measure of spread that ignores outliers, in the same way the median ignores them for the centre.
Why is the standard deviation larger than I expected?
Squaring the deviations gives large gaps disproportionate weight, so a single distant value inflates it noticeably. Compare it against the interquartile range: if they disagree sharply, you have outliers.
Which quartile method is used?
Linear interpolation across the sorted values — the same method as Excel's PERCENTILE.INC and R's default type 7. Some school syllabuses teach an exclusive-median method instead, and on small data sets the two can disagree visibly, so check which one your course expects.
Is it safe to paste confidential figures here?
Yes. The numbers are parsed and summed by JavaScript inside your own tab, with no upload, no account and nothing written to storage. Salary tables, patient measurements and unpublished results never leave the machine you typed them on.
Is Standard Deviation Calculator really free, with no limits?
Yes. There is no account, no daily cap, no file-size tier and no watermark, because there is no server cost to recover. The site is funded by clearly disclosed partner recommendations on the Partners page, never by metering the tools.
Are my files or text uploaded when I use Standard Deviation Calculator?
No. Everything is processed by JavaScript running in your browser, on your device. You can verify it: open your browser's developer tools, switch to the Network tab, and use the tool. You will see no request carrying your data — because there is nowhere for it to go.