Software like Excel can make this calculation easier. It is calculated by taking the differences between each number in the data set and the mean, then squaring the differences to make them positive, and finally dividing the sum of the squares by the number of values in the data set.
If all the data values are identical, then it indicates the variance is zero. In statistics, variance measures variability from the average or mean. Variance is always non-negative, a small variance indicates that the data points tend to be very close to the mean (expected value) and hence to each other. Variance is the measure of how notably a collection of data is spread out.
Investopedia / Alex Dos Diaz Understanding Variance
