Default WordPress Image Sizes and How to add Custom Sizes

When you upload an image, WordPress does a lot of work behind-the-scenes so you can serve the image to your visitors. You can piggyback on this process and add custom image sizes to save yourself from having to resize images manually.
In this post, I’ll explain how and why WordPress creates different image sizes. Then I’ll teach you how to add your own image sizes by modifying the functions.php file, regenerate thumbnails and add your new image sizes to the Gutenberg image block and/or the WordPress loop.
WordPress Image Sizes Explained
Every time you upload an image into the WordPress media library, these are the additional image size options WordPress creates by default:

Thumbnail
Medium
Medium Large
Large

If your theme specifies additional image sizes, WordPress creates those as well.
WordPress also preserves the original size you upload and names it Full as in full-size.
You can see all of these (with the exception of Medium_Large) in the Gutenberg image block Image Size drop down when inserting an image into a page or post.
Why does WordPress create so many images?  » Read More