Standard deviation calculator
Standard deviation measures how spread out values are around their mean. Choose "sample" when your data is part of a larger group.
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How to use it
- Enter data (separate numbers with commas, spaces or new lines) and data type.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
Population: σ = √(Σ(x - μ)² ÷ n). Sample: s = √(Σ(x - x̄)² ÷ (n - 1)).
Example
Inputs: Data type = Sample (divide by n - 1). Result: Sample standard deviation (s): 2.13809; Variance: 4.571429; Mean: 5.
Limits and caveats
- A sample needs at least two values because it divides by n - 1.
- Standard deviation is sensitive to outliers, so check extreme values first.
Questions about this tool
What is the difference between sample and population SD?
Population SD divides by n and is used when you have every value. Sample SD divides by n - 1 (Bessel's correction) to avoid underestimating the spread of the wider group.
What does a small standard deviation mean?
The values sit close to the mean. A large one means they are spread far apart.
Does it match Excel?
Yes. The sample option matches STDEV.S and the population option matches STDEV.P.