Xorg screen resolution in FreeBSD as VirtualBox Guest

After install Xorg from

/usr/ports/x11/xorg

as root edit /etc/X11/xorg.conf inserting at Section “Monitor”:

HorizSync 31-80
VertRefresh 30-100
ModelName "1600x900@60HZ"

In Section “Screen” add

DefaultDepth 24

and edit/add the resolution:

SubSection "Display"
Viewport 0 0
Depth 24
Modes "1600x900"
EndSubSection

where “Modes” is the screen proportion that you want.