Change default width of gnome-terminal and terminator windows

Terminator does allow you setting up a default size. :)

Just open the file ~/.config/terminator/config with your favorite editor. You should have a section titled [layouts]. You only need to add a line within the sub-section named [[[window0]]] belonging to the [[default]] section. My configuration file, for instance, looks like this:

[global_config]
  enabled_plugins = CustomCommandsMenu, InactivityWatch, ActivityWatch, TerminalShot, LaunchpadCodeURLHandler, LaunchpadBugURLHandler
[keybindings]
[profiles]
  [[default]]
    scrollbar_position = hidden
    visible_bell = True
    scrollback_lines = 1000000
    foreground_color = "#ffffff"
    copy_on_selection = True
    background_color = "#300a24"
[layouts]
  [[default]]
    [[[child1]]]
      type = Terminal
      parent = window0
      profile = default
    [[[window0]]]
      type = Window
      parent = ""
      profile = None
      size = 900, 600
[plugins]

The relevant part is only the line starting with "size", of course.

In terminator the GUI option for size is not there. A simple way to set up this is --

First open terminator and set the window size according to your need and comfort.

Right click and go to preference and then to layout.

Click on the terminal name under window and then save the layout.

Thats it, It will open the terminator in the same size, as you have set up, next time you open it.

I don't know about terminator, but in gnome-terminal there's an option under the profile settings to set the starting dimensions to any number of rows and columns you want, specifically Edit->Profile Preferences.