Standard Deviation Calculator
Population and sample standard deviation for any data set.
Frequently Asked Questions
What does standard deviation tell you?
It measures how spread out values are around the mean, in the same units as the data. A small SD means values cluster tightly; a large SD means they are widely scattered.
Population vs sample standard deviation – which one?
Use the population version when your data is the entire group you care about. Use the sample version (dividing by n - 1) when your data is a sample used to estimate a larger population.
How is variance related?
Variance is the average of squared differences from the mean, and standard deviation is its square root. Squaring makes all differences positive and penalises large deviations more heavily.
Is the Standard Deviation Calculator free, and is my data private?
Yes. It is completely free and every calculation runs locally in your browser, so the numbers and dates you enter are never uploaded, stored, or shared with anyone.
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