Why divide by n − 1 for a sample?

Bessel's correction: dividing by n − 1 makes the sample variance an unbiased estimate of the population variance.

Standard Deviation Calculator

Standard deviation measures how spread out data is around the mean. See the squared deviations, the variance and the square root for both sample and population.

How to use the standard deviation calculator

Enter the data values.
Choose the sample or population result depending on your data.

Examples

2, 4, 4, 4, 5, 5, 7, 9

Answer: σ = 2, s ≈ 2.138

Formulas

Standard Deviation

s = \frac{\sum ( x _{i} - x ˉ ) ^{2}}{n - 1}