Standard Deviation Calculator - Version 1.0 Standard deviation is a widely used measurement of variability or diversity used in statistics and probability theory. It shows how precise your data is.The standard deviation is the square root of its variance. A low standard deviation indicates that the data points tend to be very close to the mean, whereas high standard deviation indicates that the data are spread out over a large range of values. Variance and standard deviation depend on the mean of a set of numbers. Calculating them depends on whether the set is a population or sample.