I'm consistently using 3000x750 images for the standout images for my entries. I've recently added a new post with such image (I'm 100% sure about its size) and I've realized, that for some reason it started looking differently than others (see images below, headers for clarity):

This is a valid header image:

enter image description here

This is an invalid header image (too high):

enter image description here

This can also be seen when you scroll down to the posts themselves:

enter image description here

I opened FTP connection and figured out, that there are different sizes of thumbnails for old and new images:

Old thumbnail sizes New thumbnail sizes
1024 x 256 1024 x 256
1018 x 460
768 x 192 768 x 192
670 x 300
474 x 342
730 x 410
300 x 75 300 x 75
230 x 230
150 x 150 150 x 150

So suddenly Wordpress started generating different sizes of thumbnails than it did earlier.

My configuration is:

  • Wordpress 4.9.16 (I'm avoiding the dreaded Gutenberg this way)
  • Travelify theme
  • The website is reachable under URL https://zpowietrza.org.pl
  • Plugins:
    • Akismet antyspam
    • All in One WP Security
    • GA Google Analytics
    • Kiwi Social Share - Social Media Share Buttons & Icons
    • MetaSlider
    • Simple Lightbox
    • UserRestrictionPlugin (my own, ensures, that only two specific users are registered)
    • Zastępowanie medium (Replacing media)

So far I tried to find any theme-related settings, which relate to thumbnail sizes, but I failed to find any, which is relevant. I also tried disabling all relevant plugins before adding the header image, but it also didn't worked.

Why thumbnail images suddenly started being created in different sizes? Which component may be responsible for that?

  • I'd first get all registered image sizes and start to dig from there. Which image size is registered by which plugin and so on. Meta Slider may have introduced something behind the scenes, but it's hard to say. Commented Feb 23, 2021 at 13:08

1 Answer 1


for performance reasons, WordPress creates copies of image files in various sizes. There are three default sizes, while rest of them are usually defined by themes or plugins.

If you don't want to use the resized image, then use a full-size image while adding an image to the post.

if these are featured images, then you need to modify the code to use full size.(unless your theme has an option for it)

As far as Gutenberg considered you can install this plugin to disable Gutenberg https://wordpress.org/plugins/classic-editor/

  • 1
    You were right. The theme added its own sizes. Since old ones worked correctly, I simply commented out all custom size definitions from the functions.php and used Force Regenerate Thumbnails to... well, you can guess. Now everything works fine again. Thanks!
    – Spook
    Commented Feb 23, 2021 at 13:20
  • you are welcome
    – MMK
    Commented Feb 23, 2021 at 13:23

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