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How can I add a custom image upload size with a width of 550px and make it selected by default in the Add Media page?

Currently, there are 4 sizes available: Thumbnail, Medium, Large and Full Size. The Full Size option is selected by default.

Anyone knows a working solution to this?

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up vote 7 down vote accepted

There are a few steps to this, as I found out today. First, you add a custom image size (you can put this somewhere the functions.php file in your theme):

add_theme_support( 'post-thumbnails' );
add_image_size( 'my-size', 550, 550 ); // not sure what you want your height to
                                     // be, but this'll shrink it to 550px
                                     // wide *or* tall. If you want it to be
                                     // cropped to a 550px square, add true as
                                     // a fourth argument

The unfortunate thing is that WordPress doesn't actually show this new size in the media uploader. You'll have to put a function that does this into your functions.php as well (source: http://kucrut.org/insert-image-with-custom-size-into-post/):

function my_insert_custom_image_sizes( $sizes ) {
    // get the custom image sizes
    global $_wp_additional_image_sizes;
    // if there are none, just return the built-in sizes
    if ( empty( $_wp_additional_image_sizes ) )
        return $sizes;

    // add all the custom sizes to the built-in sizes
    foreach ( $_wp_additional_image_sizes as $id => $data ) {
        // take the size ID (e.g., 'my-name'), replace hyphens with spaces,
        // and capitalise the first letter of each word
        if ( !isset($sizes[$id]) )
            $sizes[$id] = ucfirst( str_replace( '-', ' ', $id ) );

    return $sizes;

// apply the above function as a filter on the media uploader's list of
// image sizes
add_filter( 'image_size_names_choose', 'my_insert_custom_image_sizes' );

Lastly, to set this size as the default, you'll need to change a WordPress setting. Add a filter on the setting in question. This has the benefit of being portable with your theme in which you've defined all the above options.

function my_set_default_image_size () {
    return 'my-size';
add_filter( 'pre_option_image_default_size', 'my_set_default_image_size' );

I tested this all out on WordPress 3.4.2, and it seems to work great.

Note: I'd recommend putting the above PHP code into an init function of some sort and attaching it to the 'after_setup_theme' hook:

// define the functions first
function my_insert_custom_image_sizes( $sizes ) {
    // not going to repeat the function body, for brevity's sake

function my_set_default_image_size() {
    // ditto

// define the init function next, which sets up all the necessary stuff
function custom_image_setup () {
    add_theme_support( 'post-thumbnails' );
    add_image_size( 'my-size', 550, 550 );
    add_filter( 'image_size_names_choose', 'my_insert_custom_image_sizes' );
    add_filter( 'pre_option_image_default_size', 'my_set_default_image_size' );

// and attach that init function to the 'after_setup_theme' hook
// so it runs on each page load once your theme's been loaded
add_action( 'after_setup_theme', 'custom_image_setup' );
share|improve this answer
No need for the SQL, you can use the pre_option_{$option_name} filter. Eg. add_filter('pre_option_image_default_size', function() { return 'my-size'; }); – chrisguitarguy Nov 21 '12 at 1:04
Great answer paul, thank you! – Amanda Bynes Nov 21 '12 at 11:18
@chrisguitarguy: thanks for the tip; I didn't know about that and have updated my answer accordingly. This has the added benefit of being more portable. – Paul d'Aoust Nov 26 '12 at 19:15
there is no function needed to set the default image size to a custom value: update_option('image_default_size', 'my-size' ); does the trick. but this only works with your my_insert_custom_image_sizes function, so thanks for that :) – honk31 Jun 23 '14 at 9:31

Just set all other options to 0 in your Admin panel under "Settings" » "Media". This will disable them.

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This did not answer my question, unless if I am confused. I asked: How can I add a custom image upload size with a width of 550px and make it selected by default in the Add Media page? – Amanda Bynes Sep 23 '12 at 22:29
Add a custom image size (see Codex) and then set all default ones to 0. That does answer your question. – kaiser Sep 23 '12 at 22:48
No but then the Full Size one will be selected by default. As I am sure that you already know, I cannot remove Full Size from the list and I do not want to either. How can I make so that my custom sized one is selected by default and not Full Size? – Amanda Bynes Sep 23 '12 at 22:52
Ah, ok. I understand your needs. – kaiser Sep 23 '12 at 23:14
Do you know a solution to it buddy? – Amanda Bynes Sep 23 '12 at 23:23

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