Subtitle doesn't make sense, don't try to find one.
Seems everyone has a version of this function.
Here's another one. This one is trick free and it's mine, mine, mine...
#AutoIt3Wrapper_Au3Check_Parameters=-d -w 1 -w 2 -w 3 -w 4 -w 5 -w 6
#include <WinAPI.au3>
; Make GUI
GUICreate("StringSize", 600, 400)
GUISetBkColor(0) ; black magic GUI
; First example:
Global $sLabelText = "Pa Da Pam Pam..."
Global $aLabelTextSize = _StringSize($sLabelText, 14)
GUICtrlCreateLabel($sLabelTe