How to Resize an Off Screen Window in Mac OS X

OS X, particularly recent versions of the operating system, do a good job of corralling application windows by either not allowing a user to resize a window beyond the boundaries of the screen or by automatically snapping a window to a second display for those with multi-monitor setups. But sometimes — due to errors, bugs, or when disconnecting an external monitor — an application window can get “stuck” partially or completely outside of the visible area of the Mac’s display, and getting it back can seem impossible. Thankfully, there’s a quick and easy step you can take to automatically fix an off screen window in Mac OS X, and it’s called Zoom.
The Zoom function has long been present in OS X, and it’s normally accessed by clicking the green button in the top-left portion of a window (note, however, that in OS X Yosemite the green Zoom button now takes an application into full screen mode, but you can still use the Zoom function by holding the Option key while clicking).

If you can see the green zoom button, it’s the best way to bring the missing portions of your OS X application window back into view. But what if it’s the top of the window that’s off screen, and you can’t see the zoom button at all? In that case, you can achieve the same result via an option in the menu bar.
Simply select your desired application to make it active by click on its icon in the Dock (you should see the application’s name in the top-left corner of your OS X Menu Bar, next to the Apple logo). Then, also in the Menu Bar, click the word Window and then Zoom. If you have multiple windows open in the same application, you can also select Zoom All to bring them all to the correct position at once.

As you can likely guess from its name, this has the exact same effect as the green zoom button, and your partially missing window or windows will now be automatically repositioned and resized to fit your current monitor. So the next time you unplug your external monitor and end up with a full or partial off screen window, don’t panic. Just remember Window > Zoom to bring your missing application windows back.