How to center a window on the screen in Tkinter?

You can try to use the methods winfo_screenwidth and winfo_screenheight, which return respectively the width and height (in pixels) of your Tk instance (window), and with some basic math you can center your window:

import tkinter as tk
from PyQt4 import QtGui    # or PySide

def center(toplevel):
    toplevel.update_idletasks()

    # Tkinter way to find the screen resolution
    # screen_width = toplevel.winfo_screenwidth()
    # screen_height = toplevel.winfo_screenheight()

    # PyQt way to find the screen resolution
    app = QtGui.QApplication([])
    screen_width = app.desktop().screenGeometry().width()
    screen_height = app.desktop().screenGeometry().height()

    size = tuple(int(_) for _ in toplevel.geometry().split('+')[0].split('x'))
    x = screen_width/2 - size[0]/2
    y = screen_height/2 - size[1]/2

    toplevel.geometry("+%d+%d" % (x, y))
    toplevel.title("Centered!")    

if __name__ == '__main__':
    root = tk.Tk()
    root.title("Not centered")

    win = tk.Toplevel(root)
    center(win)

    root.mainloop()

I am calling update_idletasks method before retrieving the width and the height of the window in order to ensure that the values returned are accurate.

Tkinter doesn't see if there are 2 or more monitors extended horizontal or vertical. So, you 'll get the total resolution of all screens together and your window will end-up somewhere in the middle of the screens.

PyQt from the other hand, doesn't see multi-monitors environment either, but it will get only the resolution of the Top-Left monitor (Imagine 4 monitors, 2 up and 2 down making a square). So, it does the work by putting the window on center of that screen. If you don't want to use both, PyQt and Tkinter, maybe it would be better to go with PyQt from start.


The simplest (but possibly inaccurate) method is to use tk::PlaceWindow, which takes the pathname of a toplevel window as an argument. The main window's pathname is .

import tkinter

root = tkinter.Tk()
root.eval('tk::PlaceWindow . center')

second_win = tkinter.Toplevel(root)
root.eval(f'tk::PlaceWindow {str(second_win)} center')

root.mainloop()

The problem

Simple solutions ignore the outermost frame with the title bar and the menu bar, which leads to a slight offset from being truly centered.

The solution

import tkinter  # Python 3

def center(win):
    """
    centers a tkinter window
    :param win: the main window or Toplevel window to center
    """
    win.update_idletasks()
    width = win.winfo_width()
    frm_width = win.winfo_rootx() - win.winfo_x()
    win_width = width + 2 * frm_width
    height = win.winfo_height()
    titlebar_height = win.winfo_rooty() - win.winfo_y()
    win_height = height + titlebar_height + frm_width
    x = win.winfo_screenwidth() // 2 - win_width // 2
    y = win.winfo_screenheight() // 2 - win_height // 2
    win.geometry('{}x{}+{}+{}'.format(width, height, x, y))
    win.deiconify()

if __name__ == '__main__':
    root = tkinter.Tk()
    root.attributes('-alpha', 0.0)
    menubar = tkinter.Menu(root)
    filemenu = tkinter.Menu(menubar, tearoff=0)
    filemenu.add_command(label="Exit", command=root.destroy)
    menubar.add_cascade(label="File", menu=filemenu)
    root.config(menu=menubar)
    frm = tkinter.Frame(root, bd=4, relief='raised')
    frm.pack(fill='x')
    lab = tkinter.Label(frm, text='Hello World!', bd=4, relief='sunken')
    lab.pack(ipadx=4, padx=4, ipady=4, pady=4, fill='both')
    center(root)
    root.attributes('-alpha', 1.0)
    root.mainloop()

With tkinter you always want to call the update_idletasks() method
directly before retrieving any geometry, to ensure that the values returned are accurate.

There are four methods that allow us to determine the outer-frame's dimensions.
winfo_rootx() will give us the window's top left x coordinate, excluding the outer-frame.
winfo_x() will give us the outer-frame's top left x coordinate.
Their difference is the outer-frame's width.

frm_width = win.winfo_rootx() - win.winfo_x()
win_width = win.winfo_width() + (2*frm_width)

The difference between winfo_rooty() and winfo_y() will be our title-bar / menu-bar's height.

titlebar_height = win.winfo_rooty() - win.winfo_y()
win_height = win.winfo_height() + (titlebar_height + frm_width)

You set the window's dimensions and the location with the geometry method. The first half of the geometry string is the window's width and height excluding the outer-frame,
and the second half is the outer-frame's top left x and y coordinates.

win.geometry(f'{width}x{height}+{x}+{y}')

You see the window move

One way to prevent seeing the window move across the screen is to use .attributes('-alpha', 0.0) to make the window fully transparent and then set it to 1.0 after the window has been centered. Using withdraw() or iconify() later followed by deiconify() doesn't seem to work well, for this purpose, on Windows 7. I use deiconify() as a trick to activate the window.

Making it optional

You might want to consider providing the user with an option to center the window, and not center by default; otherwise, your code can interfere with the window manager's functions. For example, xfwm4 has smart placement, which places windows side by side until the screen is full. It can also be set to center all windows, in which case you won't have the problem of seeing the window move (as addressed above).

Multiple monitors

If the multi-monitor scenario concerns you, then you can either look into the screeninfo project, or look into what you can accomplish with Qt (PySide6) or GTK (PyGObject), and then use one of those toolkits instead of tkinter. Combining GUI toolkits results in an unreasonably large dependency.

Tags:

Python

Tkinter

Centering

Recent Posts