STATISTICS / CALCULATOR
Standard Deviation Calculator.
Measure the spread of a sample or a whole population.
LET’S WORK IT OUT
Your numbers, your answer.
THE WHY BEHIND THE ANSWER
How it works.
Standard deviation describes how far values tend to lie from the mean. Select population when you have the full group, or sample for a sample estimate.
THE FORMULAPopulation variance = Σ(x − mean)² ÷ n; sample variance = Σ(x − mean)² ÷ (n − 1)
Worked example
For the population 2, 4, 4, 4, 5, 5, 7, 9, the mean is 5, variance is 4 and standard deviation is 2.
Good to know
The sample calculation requires at least two numbers. Results are rounded for display.
ONE MORE THING
Why does sample variance divide by n − 1?
The n − 1 divisor is the usual correction when estimating a population variance from a sample.