In PowerPoint 2013/2016, widescreen (16:9) is the default aspect ratio for new presentations. If you need to change the slide size to the former standard (4:3), or even a custom size that you might need for an academic poster or presentation, follow the instructions below or in the video above.

1. From the Design tab, click the Slide Size icon.
2. Select Standard (4:3) or Custom Slide Size.
   • If you selected Custom, enter your Width, Height, and other criteria in the dialog box and click OK.
3. You will receive a pop-up window stating that you’re scaling to a new slide size. Select Maximize to increase the size of your slide content when you are scaling to a larger slide size. Select Ensure Fit to decrease the size of your content when scaling to a smaller size.