Tiny grub font - small grub text - can't read grub screen
I'm new to linux and I have a brand new laptop with a crazy resolution of 3840x2400. Great to look at but OMG the grub screen! I couldn't see it without pressing my nose to the screen!
All my google searches insisted that I needed to edit the /etc/default/grub and add GRUB_GFXMODE="your screen resolutionx32" and that would fix it.
WRONG. It alone did nothing. After days of hair pulling madness and tears, I've finally found the REAL fix...
#1 - install the right font and size to the grub. (30 denotes the font size, which works for me. If you want it bigger, just increase it.).
sudo grub-mkfont -s 30 -o /boot/grub/DejaVuSansMono.pf2 /usr/share/fonts/truetype/dejavu/DejaVuSansMono.ttf
#2. Edit /etc/default/grub - use sudo nano /etc/default/grub and add GRUB_FONT=/boot/grub/DejaVuSansMono.pf2
while you're at it (and for good measure) also add your appropriate screen resolution on that same file too GRUB_GFXMODE="your screen resolutionx32" which will look something like GRUB_GFXMODE=3840x2160x32 . On the line below it add GRUB_GFXPAYLOAD_LINUX="keep". The "keep" command is important bc your grub can throw errors without it.
#3. Update your grub sudo update-grub Now reboot, sit back, and revel in the beauty of being able to actually read your grub screen!!!
You're welcome! 
credit for this fix: http://www.obeythetestinggoat.com/ot-hidpi-on-ubuntu-with-a-samsung-ativ-9.html