How to set dpi for your system

There's a couple of ways that dpi can be set for the linux system.

Add Options "DPI" "100x100" in the /etc/X11/xorg.conf file under device sections.

Section "Device"
.
.
Option "DPI" "100x100
End Section

Set display size in the xorg.conf file under section Monitor. X needs the display size in mm. So if your monitor resolution is 1360x768, then the display width for 100dpi would be 1360*.254 and for length : 768*.254

Section "Monitor"
.
.
Identifier "Monitor0"
DisplaySize 345 195 # 1360x768 100dpi
.
.
End Section

Needless to say the result rocks :)