About standard deviation calculator
Standard deviation measures how spread out numbers are around their average. A small value means the data is bunched together, and a large value means it is scattered.
What you get
- Mean, the usual average; median, the middle value; mode, the most frequent value.
- Variance, the average squared distance from the mean.
- Standard deviation, the square root of the variance, in the same units as your data.
Sample or population
Use population standard deviation when your data is everything you care about, and sample standard deviation (dividing by n − 1) when it is a sample from a larger group.
A worked example
For the numbers 4, 8, 6, 5 and 3, the mean is 5.2. The squared distances from the mean add up to 14.8. Dividing by 5 gives a population variance of 2.96 and a standard deviation of 1.72. Dividing by 4 for a sample gives a variance of 3.7 and a standard deviation of 1.92.
Reading the result
About two thirds of values in a bell-shaped data set fall within one standard deviation of the mean, and about 95 percent within two.
