dpi comparison

Monitor’s physical DPI	Automatic configuration selects the following Windows DPI value	Scale level	Effect
Less than 116	96	100%	Displays text and graphics at a smaller size.
116 to 138	120*	125%	Displays text and graphics at a medium size.
More than 138	144*	150%	Displays text and graphics at a larger size.

https://msdn.microsoft.com/en-us/library/windows/hardware/dn915348(v=vs.85).aspx

check current dpi

https://askubuntu.com/questions/378386/how-to-get-the-right-dpi-resolution-on-ubuntu-13-04-saucy

$ xdpyinfo | grep -B2 dots