Standard Deviation Calculator

Calculate mean, variance, and standard deviation for any data set. Supports both population and sample standard deviation with a full breakdown of each step.

Please provide numbers separated by commas to calculate the standard deviation, variance, mean, sum, and margin of error.

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What is Standard Deviation?

Standard deviation measures how spread out values are around the mean. A small value means data clusters closely; a large value means data is widely spread. It is one of the most important measures in statistics, finance, and research.

Population vs Sample Standard Deviation

Use population standard deviation (σ) when you have data for the entire group. Use sample standard deviation (s) for a subset of data — it uses n−1 in the denominator (Bessel's correction) to account for sampling uncertainty.

How it is Calculated

Calculate the mean, subtract it from each value and square the result, average those squared differences (variance), then take the square root. This calculator performs all steps and shows intermediate values.

The 68-95-99.7 Rule

In a normal distribution: 68% of values fall within 1 standard deviation, 95% within 2, and 99.7% within 3. This empirical rule is widely used to understand data distribution and identify outliers.