While setting up a new presentation, Sandra Mahan asked me if my slides were larger than normal. Since I had simply picked a default template, I told her I thought it was fine and it fit OK on my screen.
After some screen sharing, we found out that there's an option that determine what the screen size ratio will be when setting up a slide presentation… Design > Slide Size
Aside from setting a custom size, you can choose from the two defaults - Standard (4:3)
and Widescreen (16:9)
The numbers are the ratio of the width and height of the screen. The Standard size gives you a more boxy display, while the widescreen works well for the large screen monitors.
If you switch screen sizes, PowerPoint will ask you if you want to change the scaling of your content. I'd recommend Ensure Fit
so that all your content will still show on the slide:
I'd also recommend making the decision on your screen sizing before you get too far into your content creation, however. If you switch to the smaller slide with Ensure Fit, switching back to the widescreen format will leave your content bunched up as it was for the standard format.