Height of root window after make-frame

[martin rudalics]

If with emacs -Q I do

(let ((window (frame-root-window (make-frame))))
  (window-total-size window))

and afterwards go to the window just created and do there

(window-total-size)

the difference of the values here is two (apparently accounting for the
toolbar).  Is there any way to know the size of that window reliably and
immediately for all systems?

martin, on GNU Emacs 24.2.50.1 (i386-mingw-nt5.1.2600)
 of 2012-09-02 on MACHNO