+33659 If you have a set of numbers, xi where i runs from 1 to n, then the sample standard deviation is given by:
\(\sigma = \sqrt{\sum_{i=1}^n \frac{(x_i-\mu)^2}{n-1}}\) where \(\mu = \frac{\sum_{i=1}^n x_i}{n}\)
The above holds when you have to find the mean value from the sample. If you know the mean independently of the sample then you can replace the n-1 by n in the definition of the standard deviation.
Some calculators will automatically calculate the standard deviation for you, given a list of numbers.
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