To make Undertale full screen on Windows 10, press F4 while the game is running. Press F4 again to switch back to a window. Undertale doesn’t have a fullscreen option in its menus, so the F4 key is the built-in way to do it. On laptops where the F-keys control volume or brightness, press Fn + F4 instead.
Because Undertale was made for a 4:3 screen, you’ll see black bars on the sides of a widescreen monitor. That’s normal. Below are ways to stretch it or make it look sharper, plus fixes if F4 doesn’t work.
How to make Undertale full screen
- Start Undertale from Steam, GOG, or its desktop shortcut.
- Click inside the game window so it’s active.
- Press F4. The game fills your screen.
- Press F4 again to go back to windowed mode.
Other useful keys: hold Esc to quit the game, and use C or Ctrl to open the menu.
F4 doesn’t work? Try these fixes
- Use Fn + F4 on a laptop. Or turn on Fn Lock (often Fn + Esc) so the F-keys work as regular keys.
- Click the game window first. The key only works when Undertale is the active window.
- Close overlays. Some screen recorders, Discord overlays, or keyboard software can grab the F4 key. Close them and try again.
- Try an external keyboard if your laptop’s F4 key is mapped to a special function you can’t change.
How to get rid of the black bars (stretch to fill)
Undertale keeps its original 4:3 shape so the pixel art isn’t distorted. If you’d rather stretch it to fill a widescreen display, change your graphics card’s scaling setting:
- NVIDIA: Open NVIDIA Control Panel > Display > Adjust desktop size and position. Set Scaling mode to Full-screen and Perform scaling on to GPU. Click Apply.
- AMD: Open AMD Software > Settings > Display, turn on GPU Scaling, and set Scaling Mode to Full panel.
- Intel: Open Intel Graphics Command Center > Display and set Scale to Stretch.
Stretching makes characters look wider. Most players prefer the original shape.
Game looks blurry in fullscreen?
Undertale’s small pixel resolution gets scaled up to fit your monitor, which can look soft.
- Integer scaling: On NVIDIA (Turing GPUs and newer) and some AMD and Intel GPUs, set the scaling mode to Integer scaling in the control panel for sharp, blocky pixels. The black bars get bigger, but the image is crisp.
- High DPI setting: Right-click UNDERTALE.exe (in the game’s install folder), choose Properties > Compatibility > Change high DPI settings, check Override high DPI scaling behavior, and choose Application.
To find the install folder in Steam, right-click Undertale in your library and choose Manage > Browse local files.
Other problems in fullscreen
- Game opens on the wrong monitor: Press F4 to go windowed, press Windows + Shift + Right Arrow to move it to the other screen, then press F4 again.
- Screen flickers or goes black: In the game’s Properties > Compatibility, check Disable fullscreen optimizations. Also update your graphics driver.
- Game runs too fast or stutters: Turn on V-Sync for Undertale in your graphics card’s control panel.
Frequently asked questions
Is there a fullscreen setting in Undertale’s menu?
No. The PC version uses the F4 key to switch between fullscreen and windowed mode.
Does Undertale remember fullscreen next time?
It depends on your version and setup. If the game opens in a window, just press F4 again after it starts.
How do I make Undertale full screen on a Mac?
The same F4 key works. On a Mac keyboard, you may need to press Fn + F4.
Does this work for Deltarune too?
Yes. Deltarune also uses F4 to toggle fullscreen, and it has a fullscreen option in its settings menu.
Kermit Matthews runs Live2Tech from just outside Philadelphia. He started on a university help desk, spent years as the IT person for small businesses, and has been writing tech guides full time since 2020. Each guide is checked on a device he owns, and re-checked when a menu moves. More about Kermit.