Full screen not working on your Mac? Why, and what to do

Why is my full screen not working on Mac?

• The window does not offer it. Settings windows, some dialogs and some apps have no full screen. The green button is then grey or only zooms. Use Fill instead: hold the pointer over the green button, or drag the window to the menu bar.
• A dialog is open. A sheet or message over the window blocks full screen until you close it.
• The shortcut was changed. Another app may have taken ⌃ ⌘ F. Use the green button or the View menu, and see shortcut conflicts.
• It is a video in a web page. Browser full screen and video full screen are different: use the video player's own full screen button.

How do I force an app to go full screen?

You cannot make an app offer full screen if it has none, but you can make its window fill the screen: hold the pointer over the green button and choose Fill, or drag the window to the menu bar. Current macOS calls the second one Drag windows to menu bar to fill screen; it is in Desktop & Dock.

Why does full screen leave black bars?

The app or video has a fixed shape that does not match your screen. A 16 by 9 video on a 16 by 10 MacBook screen, like ours at 2560 by 1600, always leaves thin bars. That is the shape of the picture, not a fault.

Why will my windows not tile or fill?

On current macOS, tiling needs Displays have separate Spaces turned on in Desktop & Dock; the settings say so beside the option. It was on, at its default, on our Mac. See turning tiling off or on.

Getting back out: the full screen shortcut.

Checked on 16 October 2026 on a MacBook Air (M1) running macOS 27.0.1, by reading its settings and the labels in System Settings. Nothing was changed.