Standard Deviation Calculator
Calculate population or sample standard deviation, variance and mean of a dataset.
Last updated: August 2026
Comma-separated numbers, e.g. 2, 4, 4, 4, 5, 5, 7, 9.
Standard deviation
2.1381
Variance
4.5714
Mean
5
Sample divides by n−1; population divides by n. Use sample for a survey, population for a full census.
How it works
σ² = Σ(x − mean)² ÷ n (population) or ÷ (n−1) (sample). σ = √variance.
Example: [2,4,4,4,5,5,7,9] → σ = 2 (population).
Frequently Asked Questions
What is standard deviation?
It measures how spread out values are around the mean. A small standard deviation means values cluster tightly; a large one means they are widely scattered.
What is the difference between population and sample?
Population divides by n (you have all data). Sample divides by n−1 (you have a subset) to correct for sampling bias. Use sample for survey data.
How is standard deviation used in finance?
It measures investment volatility. A fund with a higher standard deviation has wider swings in returns — more risk.
Why does my result differ from Excel's STDEV?
Excel has two functions: STDEV.P for population and STDEV.S for sample. If your numbers are a subset of data, the sample result with n−1 matches Excel's STDEV.S.