Orthographic scale questions help!

hello i wanna render with the orthographic camera and i set up the camera view to fit the A1 format . but now i need to adjust the orthographic scale and i don’t know how to i find the perfect ratio do you guys know where i can find that? i have the same problem as this guy : orthographic scale = cm of x at 300dpi?

but i am on 2.8 and the plugin does not exist anymore