Free Online Standard Deviation Calculator

1. Paste or type the list of numbers, separated by commas, spaces, or newlines.
2. Pick sample (n − 1) for subset data or population (n) for the whole group.
3. Read the mean, variance, standard deviation, and count in the stats panel.

Standard deviation (σ) is the most common measure of dispersion. Population SD is σ = √(Σ(x − μ)² ÷ n); sample SD is s = √(Σ(x − x̄)² ÷ (n − 1)) — the n − 1 denominator is Bessel's correction, used when the data is a subset of a larger population.

For a roughly normal distribution about 68% of values fall within one σ of the mean, 95% within two σ, and 99.7% within three σ — the famous 68-95-99.7 rule that powers most quick quality-control checks.

This page returns the mean, variance (σ²), standard deviation (σ), and count. Toggling between sample and population modes is one click — the sample value will always be slightly higher because dividing by a smaller denominator inflates the result. Most spreadsheet STDEV functions default to sample, so match that mode when comparing.