Calculating the Mean To calculate the standard deviation, first find the mean by adding up all numbers and dividing by their count. For example, for 82, 93, 98, 89 and 88: (82+93+98+89+88)/5 = sum of numbers/5 = average of 90.
Standard Deviation Formula The formula to calculate standard deviation involves finding differences between each number and the mean; squaring those differences; summing them up; then dividing by n-1. Finally take square root of result to get standard deviation. For instance: (8^2 +3^2 +8^2 +1^2 +(-1)^2) /4 =142/4=35.5=square root(35.5)=standard deviation