A few weeks ago while working in Photoshop (CS4), I accidentally unselected the “resize window to fit” option & had no idea that I did so.

Since them I was trying to figure out what I did to have my open windows not zooming to the sizes that I set my documents to be so I had to resize them manually. This was a mild annoyance until today when I accidentally figured out what was causing the issue.

Had I done some quick Googling, I would have found this answer & saved myself a mini headache. Sometimes I forget the power of the internet. Duh!

Automatically resize the window when zooming

- With the Zoom tool active, select Resize Windows To Fit in the options bar. The window is resized when you magnify or reduce the view of the image.

When Resize Windows To Fit is deselected (the default), the window maintains a constant size regardless of the image magnification. This can be helpful when using smaller monitors or working with tiled views.

Note: To automatically resize the window when using keyboard shortcuts to reduce or magnify an image view, choose Edit > Preferences > General (Windows) or Photoshop > Preferences > General (Mac OS), then select the Zoom Resizes Windows preference and click OK.