Standard Deviation

Get the mean, population variance and standard deviation (σ) of a list of numbers. Paste comma-separated values to see how spread out your data is.

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💡 Good to know: In a bell curve, about 68% of values fall within one standard deviation of the mean — the "68–95–99.7" rule.

Mean: 18 · Variance: 151.666667 · σ (pop): 12.315302

Worked on the example above, step by step — follow along and you can do it on paper next time, no tool required.

Standard deviation measures spread — on average, how far the numbers sit from their mean.
First find the mean
108 ÷ 6 = 18
Average the squared distances from the mean (that's the variance)
Σ(x − 18)² ÷ 6 = 151.666667
Take the square root of the variance
√151.666667 = 12.315302

Is this population or sample σ?

Population — it divides by n, not n−1.

What does a larger σ mean?

The values are more spread out from the mean; a σ near zero means they're tightly clustered.