[Solved]-Highcharts: converting millimeters to pixel-Highcharts

• You can use some of the already existing converters to get those values, like: https://www.unitconverters.net/typography/millimeter-to-pixel-x.htm

• You can use CSS to set parameters for the container that the chart is rendered inside, demo: https://jsfiddle.net/BlackLabel/vu41gdt6/

  #container {
     height: 15rem;
     width: 15rem;
  }
  
  

• Consider use regular CSS units for the charts on you web app and change them only for printing needs.

API: https://api.highcharts.com/highcharts/chart.events.beforePrint

Useful article: Using cm/mm on the CSS of a web app that replicates paper interaction is a good practice?