Best settings for using i3 window manager with HiDPI displays.

Step 1. Add Xft.dpi to ~/.Xresources

# touch ~/.Xresources
vim ~/.Xresources

Add the following:

Xft.dpi: 144

Step 2. Use xlayoutdisplay to set a custom DPI value

alex-courtis/xlayoutdisplay - GitHub

# install xlayoutdisplay
xlayoutdisplay -p HDMI-0 -d 144

Then, copy and run the command like

xrandr \
 --dpi 144 \
 --output DVI-D-0 --off \
 --output HDMI-0 --mode 3840x2160 --rate 60 --pos 0x0 --primary \
 --output HDMI-1 --off \
 --output DP-0 --off \
 --output DP-1 --off \
 --output DP-2 --off \
 --output DP-3 --off \
 --output DP-1-3 --off \
 --output HDMI-1-3 --off \
 --output HDMI-1-4 --off \
 --output HDMI-1-5 --off \
 --output DP-1-4 --off

echo "Xft.dpi: 144" | xrdb -merge

Step 3. Change the rofi's DPI value

vim ~/.config/i3/config

- bindsym $mod+d exec --no-startup-id "rofi"
+ bindsym $mod+d exec --no-startup-id "rofi -dpi 144"

EOF