Add custom image sizes into Block Editor

Adds one or more custom defined thumbnail sizes to the Block Editor. For use in Image and Latest Posts blocks. These custom sizes come from your theme, plugins, or custom calls to add_image_size().

add_filter( 'block_editor_settings', function( $editor_settings ) {
	$editor_settings['imageSizes'][] = [
		'slug' => 'square-thumbnail-retina',
		'name' => 'Square Thumbnail Retina',
	];
	return $editor_settings;
} );

How to use

Log into a staging, development, or locally hosted clone of your site.
Install and activate the Code Snippets plugin.
Navigate to WP Admin > Snippets > Add New.
Copy and paste the code from the Description tab above.
Check to ensure formatting came over properly and no syntax errors show up in the editor.
Customize the code as desired.
Add a meaningful title and description.
Select whether to run on front-end or back-end (or both). Some snippets require both.
Click the “Save and Activate” button.
Test your site to ensure it works as expected.
Disable if any problems, or recover as necessary.
Repeat steps two onward on your live environment.

Support

Describe the issue and what you’ve observed.
Describe your expected outcome(s).
List steps to reproduce the issue.
Optionally provide screen-shot or video URLs.

Credits

We code all of our code snippets directly. Our clients provide most of the ideas and demand for the functionality provided by our code snippets.

There are several sources one can find on Google for code that has inspired or contributed to this open-source library. Here’s some main ones:

License & Disclaimer

All code snippets are licensed GPLv2 (or later) matching WordPress licensing.

Disclaimer of warranty:

Except when otherwise stated in writing the copyright holders and/or other parties provide the program as-is without warranty of any kind, either expressed or implied, including, but not limited to, the implied warranties of merchantability and fitness for a particular purpose.