Standard Deviation Formula. Standard deviation (σ) is the measure of spread of numbers from the mean value in a given set of data. Sample SD formula is S = √∑ (X - M)2 / n - 1. Population SD formula is S = √∑ (X - M)2 / n. Mean(M) can be calculated by adding the X values divide by the Number of values (N).How can you estimate the standard deviation?
First, it is a very quick estimate of the standard deviation. The standard deviation requires us to first find the mean, then subtract this mean from each data point, square the differences, add these, divide by one less than the number of data points, then (finally) take the square root.