There are two standard ways of doing box plots. One is miniums and maximums, the other is the 1.5 IQR method. The very Wikipedia article your image comes from

There are two standard ways of doing box plots. One is miniums and maximums, the other is the 1.5 IQR method. The very Wikipedia article your image comes from explains this: https://en.wikipedia.org/wiki/Box_plot#Whiskers https://en.wikipedia.org/wiki/Box_plot#Whiskers