Standard Deviation Calculator
Calculate standard deviation from a set of numbers.
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Mean (Average)
Variance
Count
Sum
Min / Max
Range
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Frequently Asked Questions
What is standard deviation?
A measure of how spread out numbers are from the mean. Low SD = numbers are close to the average. High SD = numbers are spread out.
What is the difference between population and sample SD?
Population SD divides by N. Sample SD divides by N-1 (Bessel's correction). This calculator uses sample SD (N-1).
What is variance?
Variance is the square of standard deviation. It measures the average squared distance from the mean.
How do I interpret standard deviation?
In a normal distribution: ~68% of data falls within 1 SD of mean, ~95% within 2 SD, ~99.7% within 3 SD.
When should I use standard deviation?
Whenever you want to understand the variability or consistency of a data set. Useful in finance, science, and quality control.