For example, let’s say you want to use the Hack font size 36 pt. First convert the True Type Font file to pf2:
sudo grub-mkfont --output=/boot/grub/fonts/Hack36.pf2 --size=36 /usr/share/fonts/TTF/Hack-Regular.ttf
And then add the following line to your /etc/default/grub
:
GRUB_FONT=/boot/grub/fonts/Hack36.pf2