Formula
The sample version divides the squared differences by one less than the count:
Standard deviation = √(sum of (value − mean)² / (count − 1))
The variance page uses the population version and stops before the square root.
Assumptions
- The list is a sample, so the divisor is count minus 1.
- At least two numbers are entered.
Worked example
The sample 2, 4, 4, 4, 5, 5, 7, 9 has standard deviation 2.14.
Input definitions
- Sample
- The observed numbers, separated by commas.
Limitations
This is the sample standard deviation, not the population standard deviation.
Questions
Why divide by count minus 1?
A sample uses that divisor. The population variance page divides by the full count.
Can I enter one number?
No. A sample deviation needs at least two numbers.