Collect the data values: (x_1, x_2, dots, x_n)
Compute the mean: (bar{x}=frac{1}{n}sum_{i=1}^{n} x_i)
Compute squared deviations: ((x_i-bar{x})^2)
Sum squared deviations: (sum_{i=1}^{n}(x_i-bar{x})^2)
Population standard deviation:
(sigma=sqrt{frac{1}{n}sum_{i=1}^{n}(x_i-bar{x})^2})
Sample standard deviation:
(s=sqrt{frac{1}{n-1}sum_{i=1}^{n}(x_i-bar{x})^2})
If using software/calculators, choose population vs sample based on whether you divide by (n) or (n-1)