How to set custom resolution using xrandr when the resolution is not available in 'Display Settings'

Here are the steps you need to add a new custom resolution and apply it. Following steps are for adding a 1920x1080 resolution, but you can use it for any other resolution you want. But make sure your monitor and onboard graphics support that resolution.

# First we need to get the modeline string for xrandr
# Luckily, the tool "gtf" will help you calculate it.
# All you have to do is to pass the resolution & the-
# refresh-rate as the command parameters:
gtf 1920 1080 60

# In this case, the horizontal resolution is 1920px the
# vertical resolution is 1080px & refresh-rate is 60Hz.
# IMPORTANT: BE SURE THE MONITOR SUPPORTS THE RESOLUTION

# Typically, it outputs a line starting with "Modeline"
# e.g. "1920x1080_60.00"  172.80  1920 2040 2248 2576  1080 1081 1084 1118  -HSync +Vsync
# Copy this entire string (except for the starting "Modeline")

# Now, use "xrandr" to make the system recognize a new
# display mode. Pass the copied string as the parameter
# to the --newmode option:
xrandr --newmode "1920x1080_60.00"  172.80  1920 2040 2248 2576  1080 1081 1084 1118  -HSync +Vsync

# Well, the string within the quotes is the nick/alias
# of the display mode - you can as well pass something
# as "MyAwesomeHDResolution". But, careful! :-|

# Then all you have to do is to add the new mode to the
# display you want to apply, like this:
xrandr --addmode VGA1 "1920x1080_60.00"

# VGA1 is the display name, it might differ for you.
# Run "xrandr" without any parameters to be sure.
# The last parameter is the mode-alias/name which
# you've set in the previous command (--newmode)

# It should add the new mode to the display & apply it.
# Usually unlikely, but if it doesn't apply automatically
# then force it with this command:
xrandr --output VGA1 --mode "1920x1080_60.00"

Original source: https://gist.github.com/debloper/2793261

I also wrote a script that does all these steps automatically. You can try it out if the above steps seem too complicated for you: https://gist.github.com/chirag64/7853413

The option --size/-s can be used:

xrandr -s 1440x900

Should work with RandR version 1.1 or newer.

I had the same problem. In Display setting maximum resolution was 1280x720. So:

1. using xrandr command I have seen name of this monitor and resolution list.
2. I 've executed the script: xrandr --output {name of monitor} --mode {resolution}

For example:

xrandr --output DP-2-1 --mode 2560x1440