# How do you calculate standard deviation?

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$s^2 = \frac{\sum_{i=1}^n \left(x_i - \overline{x_i} \right)^ 2}{n-1}$

Where:

• $s$ in the sample variance.
• $n$ is the number in your sample.
• $x$ is each value in the sample.
• $\overline{x}$ is the sample mean.

If you don't understand that.

• You subtract the average from a number in your sample and square it.
• Do the same for each number in your sample and add up all the answers you get.
• Divide by 1 less than the number of numbers in your sample.