Free tool
Standard deviation calculator
See how spread out a set of numbers is.
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How it works
How it works
Subtract the mean from each value, square the differences and add them. Divide by n for a population or n - 1 for a sample, then take the square root for the standard deviation.
Example: for the eight values 2, 4, 4, 4, 5, 5, 7 and 9, the mean is 5. The squared differences add to 32. Treated as a whole population, the variance is 32 / 8 = 4 and the standard deviation is 2. Treated as a sample, the variance is 32 / 7, about 4.57, and the standard deviation is about 2.14.
FAQ
About this calculator
Sample or population?
Use population when you have every value in the group. Use sample when your numbers are a subset used to estimate a larger group.
What does it tell me?
A small value means the numbers cluster near the mean. A large value means they are spread out.
How many numbers do I need?
At least two for a sample and at least one for a population.
Is anything saved?
No. The math runs in your browser and nothing you enter is sent to us.
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