Standard Deviation Calculator
Compute population and sample standard deviation, variance and mean with step-by-step results. Free stats calculator.
Sample SD uses n−1 (Bessel's correction) and is the right choice when your data is a sample of a larger population.
Frequently asked questions
- Population or sample — which do I need?
- Use population SD when you have data for every member of the group. Use sample SD when your numbers are a sample drawn from a bigger group — most real datasets.
- Why n−1 instead of n?
- Bessel's correction. Sample means vary more than the true population mean, so dividing by n−1 gives an unbiased estimate.
- What does a large SD tell me?
- That values are spread widely around the mean. A small SD means they cluster tightly.
This tool runs entirely in your browser. No data is uploaded anywhere.