Standard Deviation Calculator
Measure how spread out your numbers are — with the mean included.
Calculate the standard deviation of any list of numbers to see how spread out the values are around the mean. The calculator shows the mean alongside, so you get the full picture of your dataset in one step.
How it's calculated
This calculator uses the population standard deviation: the square root of the average squared distance of each value from the mean. A small value means the numbers cluster tightly; a large one means they are spread out.
Frequently asked questions
What does the standard deviation tell me?
It measures spread. A low standard deviation means values cluster near the mean; a high one means they are widely scattered. The classic dataset 2, 4, 4, 4, 5, 5, 7, 9 has a mean of 5 and a standard deviation of 2.
Population or sample standard deviation?
This calculator uses the population formula (divides by N). If you need the sample formula (divides by N−1), multiply the result by √(N/(N−1)).
Can the standard deviation be negative?
No — it's a square root of squared distances, so it's always zero or positive. Zero means every value is identical.