Standard Size Windows Screen
Change the slide size from widescreen (16:9) to standard (4:3), or from standard to widescreen
First, make sure you're in Normal view (on the View tab, click Normal). Then click the Design tab, and click Slide Size in the Customize group.
Tip: The Slide Size button is also available in Slide Master view on the Slide Master tab.
Click Standard (4:3) or Widescreen (16:9).
When PowerPoint is unable to automatically scale your content, it will prompt you with two options:
Maximize: Select this option to increase the size of your slide content when you are scaling to a larger slide size. Choosing this option could result in your content not fitting on the slide.
Ensure Fit: Select this option to decrease the size of your content when scaling to a smaller slide size. This could make your content appear smaller, but you’ll be able to see all content on your slide.
The 16:9 widescreen setting is the default value for new presentations you create. When you change the slide size for a presentation, the size you choose only applies to that presentation. However, you can make it easy to create a new 4:3 presentation for yourself whenever you want—by defining a custom theme that uses the 4:3 aspect ratio. See below.
Resize your slides to custom dimensions and other common paper and screen sizes, including Outline
First, make sure you're in Normal view (on the View tab, click Normal). Then on the Design tab, click Slide Size, and then click Custom Slide Size.
Do one of the following in the Slide Size box:
Set the height and width dimensions, and the orientation.
Click the down arrow next to Slides sized for, and pick an option.
There are two options for 16:9 aspect ratios: Widescreen and On-screen Show (16:9). Here's the difference between the two:
On-screen Show (16:9) sets the slide dimensions to 10 in x 5.625 in.
Widescreen sets it to 13.333 in x 7.5 in.
Both of these options are the same aspect ratio so they will look the same in Normal View, since we automatically adjust the zoom. Widescreen (13.333 in x 7.5 in.) provides more slide surface area for the content, so that is the best choice for presentations. There are some other things to consider however, Widescreen (13.333 in x 7.5 in.) won’t fit on an 8.5 x 11 sheet of paper without you having to scale it.