Standard Deviation Calculator
Population and sample standard deviation, variance and standard error.
How it works
Standard deviation is the typical distance of a value from the mean: square the deviations, average them, take the square root.
The sample version divides by n-1 rather than n. That correction exists because a sample's own mean sits closer to its own points than the true population mean does, which biases the estimate downward. Use the sample formula unless you genuinely have every member of the population.
Common questions
Sample or population?
Sample, almost always. Use population only when your data is the entire group you care about — every employee, every product made — not a subset you are generalising from.