Depending on the display you’re using to present your Google Slide presentation on, you may need to adjust the slide size and aspect ratio. Fortunately, Google Slides makes this easy. Follow these steps:
- Open your Google Slides presentation.
Open your presentation. - Select the File tab and choose Page setup. The Page setup dialog box will open up.
Go to File > Page Setup. - By default, the slide aspect ratio is set to the Widescreen 16:9 option. To change it, click the dropdown arrow. You can choose from Standard 4:3, Widescreen 16:9 (Default), Widescreen 16:10, and Custom options. In this guide, we’ll choose Standard 4:3. Then select Apply.
Click the dropdown arrow. SSlide sizes that you can choose from.
Select Standard 4:3 from the options and click Apply. 
Standard (4:3) Slide size. - If you’ve selected Custom, a new set of input fields will appear. Enter your desired width, height, and units. In this step, we’ll change it to 13.3 x 7.5 inches (default custom size)—Click Apply to confirm.SSelect Custom and enter your desired slide dimensions. Then, click Apply.
Default custom slide size (13.3 x 7.5 inches).