Sources:

• https://wpmudev.com/blog/wordpress-image-sizes/
• https://kb.hrcws.nl/change-or-stop-divi-image-size-thumbnail-generation/

When you upload an image to WordPress, the system keeps the original file as is and generates several additional file sizes:

By	Width	Height	Name	Type	Note
Divi	400	516	et-pb-gallery-module-image-portrait	Cropped
Divi	1280	…	et-pb-image–responsive–desktop	Scaled	Srcset Image
Divi	480	…	et-pb-image–responsive–phone	Scaled	Srcset Image
Divi	980	…	et-pb-image–responsive–tablet	Scaled	Srcset Image
Divi	400	284	et-pb-portfolio-image	Cropped
Divi	1080	…	et-pb-portfolio-image-single	Scaled
Divi	510	382	et-pb-portfolio-module-image	Cropped
Divi	400	250	et-pb-post-main-image	Cropped
Divi	1080	675	et-pb-post-main-image-fullwidth	Cropped
Divi	2880	1800	et-pb-post-main-image-fullwidth-large	Cropped
WP	768	…	medium_large	Scaled
WP	1536	…	???	Scaled
WP	2048	…	???	Scaled
WP	2560	…	big_image_size_threshold (filename-scaled)	Scaled	Media library preview if original is larger
WP	Original	Original	Uploaded image	Original
WP	Set Media	Set Media	Large	Scaled	Set 1280×1280 Media library thumb
WP	Set Media	Set Media	Medium	Scaled	Set 1920×1920
WP	Set Media	Set Media	Thumbnail	Cropped	Set 300×300

• Use a plugin like Imsanity to reduce the size of the originally uploaded image and save disk space.
• WordPress generates 3 additional file sizes as specified in WP admin » Settings » Media.
• Your theme can generate additional file sizes.
• Plugins can generate additional file sizes.

My preferred settings to reduce the number of additional image files that are generated:

• Imsanity
  • 1920×1920 or 1536×1500 (1536 is a Divi size)
• WP admin » Settings » Media
  • Thumbnail size: 300×300 (Divi size)
  • Medium size: 1280×1280 (Divi sizes)
  • Large size: 1920×1920* or 1536×1500 (same as Imsanity)