The Right DPI

TL;DR Do not assume X11 is using the correct DPI for your screen. If your fonts look blurry and ugly, X11 might be using the wrong DPI value.

I recently installed ArchLinux on my brand new Lenovo T590. (Second Thinkpad in a row and I couldn’t be happier with the choice.)

The new computer has a FHD screen (1920x1080) and when I first started using it I was rather disappointed with font rendering: fonts looked blurry and I could see anti-aliasing trying its best but not being quite up to the point. Lucida fonts, in particular, looked so ugly I couldn’t use them.

Coming from a UHD display I thought the problem was with the hardware.

ArchWiki to the rescue! By consulting the page about Xorg

• I realized with xrandr and xdpyinfo that X11 was assuming the screen was 50 cm wide and set the dpi to 96¹
• I created the file /etc/X11/xorg.conf.d/90-monitor.conf with the following data:

Section "Monitor"
   Identifier    "<default monitor>"
   # Is it better to fake actual size to ensure a multiple of 96, such as 146
   #   DisplaySize   344 194
   DisplaySize   334 187
EndSection

reboot … and voilà, nice fonts all over the screen!