Tkinter Layout Best Practices: One Manager per Container, Predictable Geometry with sticky, fill, expand, pack_propagate

Stop Tkinter windows from stretching or snapping after image load. Learn how mixing pack and grid breaks layout, and how geometry propagation fixes it.

When a Tkinter interface looks chaotic at startup and only snaps into place after an interaction like uploading an image, that’s almost always a sign of layout mismanagement. In this case, the UI stretches to near full screen before the image is loaded and only then appears correctly sized. The culprit is the way layout managers are combined and how widget geometry is allowed to propagate.

Problem example

The following snippet builds a window with a button, some controls, and a frame intended to show a loaded image. The UI appears distorted before the image is uploaded and changes size after the upload action.

from tkinter import filedialog, ttk
from tkinter import *
from PIL import Image, ImageTk
import numpy as np
# cache for image reference so it isn't garbage collected
thumb_ref = None
# open image and display it in the label
def handle_open():
    global thumb_ref
    path = filedialog.askopenfilename()
    if path:
        pic = Image.open(path)
        thumb_ref = ImageTk.PhotoImage(pic)
        if thumb_ref.width() < 1200 or thumb_ref.height() < 600:
            lbl_preview.image = thumb_ref
            lbl_preview.config(image=thumb_ref)
# build UI
root = Tk()
pane_img = Frame(root)
lbl_preview = Label(pane_img, width=1200, height=600)
btn_upload = Button(root, text='Upload Image', command=handle_open)
lbl_size = Label(root, text="Text size:", font=('calibre',12,'bold'))
cmb_size = ttk.Combobox(root, font=('calibre',12,'normal'), values=list(np.arange(8, 51, step=7)))
lbl_rot = Label(root, text="Rotation:", font=('calibre',12,'bold'))
ent_rot = Entry(root, font=('calibre',12,'normal'))
lbl_op = Label(root, text="Opacity:", font=('calibre',12,'bold'))
sld_op = Scale(root, from_=0, to=100, orient='horizontal')
# placements
pane_img.grid(column=3, row=2, columnspan=5, rowspan=10, padx=50)
lbl_preview.pack()
btn_upload.grid(column=1, row=1, padx=60, pady=60)
lbl_size.grid(column=1, row=2)
cmb_size.grid(row=2, column=2)
lbl_rot.grid(row=3, column=1)
ent_rot.grid(row=3, column=2)
lbl_op.grid(row=4, column=1)
sld_op.grid(row=4, column=2)
root.mainloop()

What’s really going on

Two things are at play. First, mixing layout managers within the same container is not allowed and leads to conflicts. The reliable pattern is to use one manager per container and nest containers where you need different behavior.

You’re mixing multiple layouts that can’t be used simultaneously within a widget.

Second, even with the correct manager, widgets may expand or shrink to fit their children unless told otherwise. Proper use of sticky in grid along with fill and expand in pack, and controlling size propagation where needed, ensures predictable geometry. Disabling geometry propagation for the image area avoids it shrinking or ballooning based on whether the image is present.

Solution and corrected example

The revised structure uses two frames placed side by side with pack. The left frame uses grid for the controls. The right frame hosts the image label and disables geometry propagation so the layout doesn’t hinge on whether an image has been loaded.

from tkinter import filedialog, ttk
from tkinter import *
from PIL import Image, ImageTk
import numpy as np
class UiShell(Tk):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.title('Example')
        w = self.winfo_screenwidth()
        h = self.winfo_screenheight()
        self.geometry(f"{w}x{h}")
        self.minsize(1200, 600)
        self._build_ui()
    def _build_ui(self):
        self.panel_controls = Frame(self)
        self.panel_preview = Frame(self)
        # keep the preview panel from resizing to its contents
        self.panel_preview.pack_propagate(False)
        self.panel_controls.pack(side='left', fill='y', padx=8, pady=8)
        self.panel_preview.pack(side='left', fill='both', expand=True)
        # right side: image area
        self.img_holder = Label(self.panel_preview)
        self.img_holder.pack(fill='both', expand=True)
        # left side: controls
        self.btn_open = Button(self.panel_controls, text='Upload Image', command=self.on_pick_image)
        self.lbl_size = Label(self.panel_controls, text="Text size:", font=('calibre',12, 'bold'))
        self.cmb_size = ttk.Combobox(self.panel_controls, font=('calibre',12, 'normal'), values=list(np.arange(8, 51, step=7)))
        self.lbl_angle = Label(self.panel_controls, text="Rotation:", font=('calibre',12, 'bold'))
        self.ent_angle = Entry(self.panel_controls, font=('calibre',12, 'normal'))
        self.lbl_opacity = Label(self.panel_controls, text="Opacity:", font=('calibre',12, 'bold'))
        self.sld_opacity = Scale(self.panel_controls, from_=0, to=100, orient='horizontal')
        self.btn_open.grid(column=0, row=0, sticky='nsew', columnspan=2, pady=8)
        self.lbl_size.grid(column=0, row=1, sticky='nsew', pady=4)
        self.cmb_size.grid(column=1, row=1, sticky='nsew', pady=4)
        self.lbl_angle.grid(column=0, row=2, sticky='nsew', pady=4)
        self.ent_angle.grid(column=1, row=2, sticky='nsew', pady=4)
        self.lbl_opacity.grid(column=0, row=3, sticky='nsew', pady=4)
        self.sld_opacity.grid(column=1, row=3, sticky='nsew', pady=4)
    def on_pick_image(self):
        fp = filedialog.askopenfilename()
        if fp:
            im = Image.open(fp)
            photo = ImageTk.PhotoImage(im)
            if photo.width() < 1200 or photo.height() < 600:
                self.img_holder.image = photo
                self.img_holder.config(image=photo)
if __name__ == '__main__':
    app = UiShell()
    app.mainloop()

Why it’s worth knowing

Layout behavior dictates whether your Tkinter UI looks stable or seems to rearrange itself as data arrives. Understanding that pack and grid must not be combined in the same parent, and knowing when to use sticky, fill, expand, and pack_propagate, prevents subtle bugs that only surface under certain runtime conditions, like loading the first image.

Wrap-up

Keep a single layout manager per container, split your UI into nested frames when you need different managers, and control geometry propagation where the content size fluctuates. With these practices, the interface will render predictably both before and after the image is loaded, and you won’t be surprised by windows that suddenly stretch or collapse.