Understanding what image aspect ratio is will help you to design your Divi website in a better way. An aspect ratio is the proportion of the width and height of your image. There are 3 common aspect ratios we use for our images, these are 16:9, 4:3 and 3:4. The most popular of these 3 is 16:9. Your Divi website consists of multiple row and column structure. With this cheat sheet you will have all of the right image measurements you can use for each column structure at a glance.
Source: Divi image sizes