I uploaded one image with size of 1920*1200 and I checked the backend Media options as followed

Thumbnail size 150 150 Medium size 300 300 Large size 1024 1024

The upload directory was supposedly has four images there,the original image,thumbnail image,Medium image,Large image,four in total,however,5 images found there with an unknown size of 825x510,my question is how this 825*510 came out and where can I config and change the size of it?

2 Answers 2


I figured it out this was a theme option located in the functions.php file

set_post_thumbnail_size( 825, 510, true );

This is how this customized size came out in the first place!

  • Additionally, your should know that set_post_thumbnail_size is for post featured image, don't consfuse with the thumbnail image (150x150 in your case).
    – cybmeta
    Feb 9, 2015 at 11:20

Just to add to this, for anyone else who might need or want the info...

You can use the $_wp_additional_image_sizes global to find out if you have any additional image sizes set by theme or any plugins.

If these additional images sizes are not needed, you can use remove_image_size($name); function and pass the $name variable from the returned array and remove the sizes not required.

I add this to my functions file to print out a list of any additional custom image sizes being created:

function royal_list_additional_image_sizes(){

    global $_wp_additional_image_sizes;

    echo '<pre>';
    print_r( $_wp_additional_image_sizes );
    echo '</pre>';



You can then use the remove_image_size($name); function in your functions file as well to remove these additional image sizes. Find more on the WordPress Codex.

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