Standard Deviation Calculator

Calculate standard deviation, variance and mean for a data set.

Sample standard deviation

2.1381

Variance: 4.5714
Mean: 5
Count: 8
Sum of squares: 32

Sample standard deviation2.1381

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How it works

Standard deviation measures how spread out numbers are from their mean. Use the sample version when your data is a subset of a larger group, and the population version when you have every value.

Formula

σ = √(Σ(x − μ)² ÷ N)
s = √(Σ(x − x̄)² ÷ (n − 1))

Example

For 2, 4, 4, 4, 5, 5, 7, 9: mean = 5, population SD = 2, sample SD ≈ 2.138.

Assumptions & limitations

Results are rounded for display.

Frequently asked questions

Sample or population?

If you measured everyone you care about, use population. If you measured a sample to estimate a bigger group, use sample.