The 68-95-99.7 Rule

The figure below will help you to visualize the 68-95-99.7 Rule (or the Empirical Rule) for a Normal Distribution. The histogram displays 100 data values from a population N(0,1). The histogram is centered on the mean of the data. The width of each bin is the standard deviation of the data. Therefore, the bin boundaries are z-scores. The numbers on each bin is the number of data values in the bin. Since there are 100 data values, these numbers are percents.