Divi makes adding images to your website easy. The challenge for some however, is knowing the correct image sizes to use in each instance. There is no standard “perfect” size for all websites because each website is different. But, there are some things you can do to make sure your images are a good fit for your Divi site.
Use this article to help you figure out the right image size for your site- The Ultimate Guide to Using Images Within Divi.
I use this handy tool when I need to figure out an aspect ratio for resizing.