Ubuntu 18.04 not detecting monitor size properly

Question

I just fresh installed Ubuntu 18.04, after some hassle I was able to install the nvidia-driver-396. I run a dual monitor setup being one a 29" ultra wide and one 24" 1080p, when I had Ubuntu 16.04 the system detected the monitors sizes without a problem, but for some reason on Ubuntu 18.04 the 29" is being detected as 34" and the 24" is being detected as 7", odd thing is that their resolutions are correct it is just the monitor size that is wrong.

VLC for some reason had huge icons on the "detected 7" monitor", I solved that by adding QT_AUTO_SCREEN_SCALE_FACTOR=0 in /etc/environment and /etc/profile.d/gnome-qt.sh

Although that solved the VLC issue the monitors sizes are still being wrongly detected, how can I solve it?

Here are some Screen Shots

This is the 29" monitor:

This is the 24" monitor:

Info on the nvidia driver:

Answer 1

This problem does not seem to be linked to drivers, since I use the open source drivers for my internal Intel video card (Core i7). It is connected via HDMI directly.

Seems that many (all?) Samsung monitors are detected as 7". Mine is 32" big, but still detected as 7" (UE32B7090).

I filed a bug: https://bugs.launchpad.net/ubuntu/+source/gnome-shell/+bug/1792167

Answer 2

I had a similar issue. I have a lapotop with an external 23" monitor and used to work fine in ubuntu mate 16.04. When I updated to ubuntu mate 18.04 it was detected as 142" and everything look zoomed. I run

export QT_AUTO_SCREEN_SCALE_FACTOR=0

then reboot and the monitor was detected right! This was my source: https://ubuntuforums.org/showthread.php?t=2390362 Hope this help!