How do I get the width and height of a Tkinter window?
You use the winfo_width method of the widget to get the actual width. You can use winfo_reqwidth to get the size that the widget is requesting, which may be different.
Note that if you call this before the window appears on the screen, you won't get the answer you expect. Tkinter needs to have actually drawn the window before it can know the size. A simple fix if you're trying to get the window size before your program starts is to call the update method on the window before trying to get the size.
Get Tkinter Window Size