In ubuntu gnome the default terminal size is 80*24 which is unsuitable for widescreen-display.This tutorail shows how to change this default startup size in ubuntu gnome.
In terminal,type this command to edit /usr/share/vte/termcap/xterm:

sudo gedit /usr/share/vte/termcap/xterm 

Find out following and change the two numbers:

:co#80:it#8:li#24\

change 80 and 24 to the number as you want (here 80 is the width,24 is the height)