Images take up a lot of storage space. Such space is limited, and we need to be frugal in using it. WordPress does some strange things when uploading an image.
Before I go into details, however, I want you to compare two images here. Move the slider back and forth and see the difference in image quality.
On another site, a self-hosted one, where I can see the image files and the amount of space each takes up, I ran an experiment. I uploaded the above photo in the full size as produced by my smartphone. The image size was 4032 x 3024 pixels, pretty typical for phones these days. The file size was 9.96 MB. The WordPress upload process created eight (yes, eight) additional files in various sizes. Together they took up 12.7 MB of storage space.
After uploading the WordPress Media Library only shows one image. It won’t be the original if it was a typical smartphone size, but a “scaled” version with a size of 2560 pixels (larger dimension). The original is not used on any post or page.
In the WordPress Dashboard Settings section for Media there are size specifications for Thumbnail, Medium, and Large. I set all of them to 0 (zero). This eliminated the generation of those extra files.
I used the same photo and scaled it down to a max width of 1200 pixels. The file size was 1.09 MB. The uploader created only one additional file and its size was just 0.13 MB, Total space used 1.22 MB.
Yes, the scaled photo took up less than a tenth the space of the original. Can you tell that much of a difference in quality in the above photos?
Moral: Don’t just upload your photos from your phone or camera, scale them down. A 1200 pixel wide photo is perfectly adequate in any post or page. WordPress neve uses anything above 2560 pixels.
.:. © 2024 Ludwig Keck
This 'n That 
Interesting read.
Thank you.
My humble opinion is that an image need not be more than 50 Kb.
Whether it’s a cellphone, tablet or iPad- seeing the image with this size makes no difference and for all web related activities, one can upload images of approximately 50kb. (it’s a different matter if one is into photography competitions).
Photography software tools can bringdown your mobile photo of 2 Mb to 50 kb.
My images rarely go beyond 100 kb.
Whether it’s 50 kb or 1.2 Mb or more, you won’t find great difference in web world.
Beginners exhaust their storage space faster because they fail to reduce their image size significantly.
If your blog or website shows only modest size images, then you can indeed save a lot of file space by sizing your images down to about 700 pixels max, as you are doing. You can also use a modest quality setting (more compression) that reduces the file size significantly. But keep in mind that WordPress makes additional images that may in fact take up more space. On my site it made extra 768×576 images that take up 130 MB each. Indeed, these additional smaller sized images can have larger fie sizes than the original.
Thank you for this knowledge and making me aware of it.
I’ve actually used 700×700 for years and just recently dropped it to 600×600. Just to save on space. I’ve used 50% of my memory (13 gig) in wordpress in 10 years of blogging. An advantage that has no one will ever be able to copy that photo and print out a big photo of it.
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This is great information, thank you!
Thank you, that was really great advice. I usually edit my pictures to a square before posting, but I should be more aware of the size too. I will be more careful.