Accepted answer

You need to make a use of formatter:

formatter: function(){
              return this.value/1000000 + "M";



To utilize the built in "shortening" functionality you can just remove your yAxis.label.format. You have currently set it to {value}, which is the default, but manually setting it seems to prevent the metric prefixes from being applied.

Look at this JSFiddle example, where all I've changed is removing the following line from both of your y-axis labels:

format: '{value}'

With this automatic shortening the following metric prefixes may be applied:

[ "k" , "M" , "G" , "T" , "P" , "E"]

You can set your own values with the lang.numericSymbols option (API).

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