Standard Deviation Calculator
Calculate population and sample standard deviation from a data set.
What is Standard Deviation?
The standard deviation is the square root of the variance, which puts the spread back into the units of the data. That is what makes it readable: a mean of 23.1 with a standard deviation of 7.4 says the typical value is 23 ± 7, and for roughly bell-shaped data about 68% of values fall within one standard deviation and about 95% within two.
How it works
One pass produces the mean and the sum of squared deviations; dividing by n or n − 1 and taking the square root gives both forms. The page also marks which values fall inside one standard deviation of the mean, so the 68% rule can be checked against the actual list rather than taken on faith.
- Enter your input. Type or paste your input into the field above — the tool responds instantly.
- Review the result. Output updates live as you type. Everything runs entirely in your browser.
- Copy or download. Use the Copy button to grab the result, or Download to save it as a file.
Examples
Realistic sample
Type or paste any realistic input — the tool computes the result locally and instantly.
Common mistakes
Expecting a server round-trip
Nothing is uploaded — every tool in this category runs entirely in your browser.