Standard Deviation Calculator
Calculate mean, variance and standard deviation from a list of numbers.
Standard deviation measures how spread out a set of numbers is from the average — a small standard deviation means values cluster tightly; a large one means they're scattered widely.
Sample vs. population — which do I need?
Use "population" when your data represents an entire group you care about. Use "sample" when your data is a subset used to estimate a larger population — the sample formula corrects for the extra uncertainty of working from a subset.
Frequently asked questions
What does a standard deviation of zero mean?
It means every value in your dataset is identical — there's no variation at all.
How is standard deviation different from variance?
Variance is standard deviation squared — standard deviation is more commonly used because it's in the same units as your original data.