Set exact size for 120 dpi and add how to find it

arch-config/per-device/lupusregina/10-monitor.conf

@@ -1,5 +1,5 @@
 Section "Monitor"
     Identifier "DisplayPort-1"
     #DisplaySize 598 336 # In millimeters
-    DisplaySize 554 311 # In millimeters
+    DisplaySize 541 304 # In millimeters
 EndSection

arch-config/per-device/lupusregina/README.md

@@ -5,3 +5,20 @@ The following parts are modified:
 - Polybar (.config/polybar/i3config.ini)
 - Xresources (.Xresources)
 - X11 (/etc/X11/xorg.conf.d/ _new files_)
+
+## Calculate Monitor size for desired DPI
+
+To get the exact monitor size xorg wants for a target dpi, execute this command.
+
+```sh
+xrandr --dpi [DPI]
+```
+
+Querying the set dpi now yields the exact monitor size you'd want to set.
+
+```
+$> xdpyinfo | grep -B 2 resolution
+screen #0:
+  dimensions:    2560x1440 pixels (541x304 millimeters)
+  resolution:    120x120 dots per inch
+```