Image Sizes

In this tutorial we are going to talk about image sizes in WordPress. Well, but what image sizes are exactly?

All right, if you open your WordPress /wp-content/uploads directory, you might find something like this there:

default image sizes in WordPress
All of these – are default WordPress image sizes.

As you can see, an image you’ve uploaded once was duplicated multiple times with different image sizes. And in this case I am just using default WordPress theme with no plugins installed.

Users who don’t know what is the thing – image sizes in WordPress could be terrified by what they see in uploads directory.

The key idea is that when you upload an original image (especially unoptimized, up to 10MB) it would stupid to use this exact file everywhere on the website. Maybe you have a list of recent posts displayed somewhere with 100×100px thumbnails and what about srcset and sizes attributes of course?

A great example is the list of products in WooCommerce in admin area:

Product list in WooCommerce admin
Image sizes here are barely 50×50px, what do you think will happen with page load time if we try to display originals instead?

Needless to say that using image resizing software is also not a great idea because it will create huge performance issues on your server.

That’s why WordPress creates so many image copies and in this tutorial we are going to learn to manage them.

Default Image Sizes

Image sizeDescription
thumbnailThumbnail size from Settings > Media.
mediumMedium size from Settings > Media.
medium_largeThis image size appeared in WordPress 4.4 with responsive images feature and is used in srcset attribute. It has a fixed width of 768px and proportional height.
largeLarge size from Settings > Media.
1536x1536 and 2048x2048These image sizes appeared in WordPress 5.3, their goal is also to generate more suitable srcset and sizes attributes on larger, high-density devices.
-scaledThis is not exactly an image size but since WordPress 5.3 if you upload an image and its height or width is more than 2560px (can be changed with big_image_size_threshold hook), then WordPress will create its smaller copy with -scaled suffix.
fullThe original image.

Thumbnail, medium and large sizes can be managed in Settings > Media:

WordPress Media settings page

Registering Custom Image Sizes

1. add_image_size()

Registering a custom image size for your need is as easy as to use add_image_size() function inside functions.php or wherever you need. But there could be a couple of nuances, we are going to discuss them in just a little bit.

Example of registering a custom image size:

add_action( 'after_setup_theme', function() {
	
	add_image_size( 'my-image-size-name', 200, 200, array( 'left', 'top' ) );
	
} );

A couple moments to keep in mind:

  • It is recommended to use add_image_size() function inside after_setup_theme hook, but usually it works great without it as well.
  • The first three parameters of the function are quite straightforward, the fourth argument is the most interesting one, it defines the rules how images with different ratio should be cropped. To keep the things simple I decided to use a square size in this example. So, it is easy to say, that if an original image is horizontal, the left part of the image will remain untouched, but the right part will be cropped, and the same I can say about vertical images – the bottom part of images will be cropped. But you can set this argument to false and images won’t be cropped, only resized. Of course you can read more about function parameters in the official documentation.
  • Don’t create a lot of custom image sizes though because more image sizes you create – more files will be in your uploads folder and more time it will need to upload (and process) an image to your site.

2. Add your custom image size selection to Media Uploader and Block Editor

When you insert images to posts, WordPress allows you to choose what image size to use:

image block settings – image size selection dropdown
Image block settings

But what should we do so our custom image size appears there? The hook image_size_names_choose should help you with that.

add_filter( 'image_size_names_choose', function( $sizes ) {
	
	// $sizes[ 'image size name' ] = 'Label (anything)';
	$sizes[ 'my-image-size-name' ] = 'Misha size';
	return $sizes;
	
} );

3. Regenerate old media

The key moment you should always remember is when you create or remove image sizes the new file copies are going to be created only at the moment of uploading an image.

What should we do in this case? Reupload images every time? Of course not, there are a plenty of plugins for that purpose. For example these ones I used:

  • AJAX Thumbnail Rebuild,
  • Force Regenerate Thumbnails.

In some cases you may want to regenerate thumbnail programmatically, you can do it with the function below:

function rudr_regenerate_sizes_for_image( $attachment_id ) {
	$path = get_attached_file( $attachment_id );
	if( $path ) {
		wp_update_attachment_metadata( 
			$attachment_id, 
			wp_generate_attachment_metadata( $attachment_id, $path ) 
		);
	}
}

Conditional image sizes registration – how to create certain image sizes for custom post types only?

Let’s imagine for a moment that your website has 10 registered custom post types, and each of them uses 2-3 image sizes on the website pages. It is easy to understand that when we upload any picture WordPress is going to create 20-30 copies of it!

There is no way to use add_image_size() for a custom post type but here is a tricky piece of code that solves this problem. This code tells WordPress when a file for a specific image size should be created and when it shouldn’t.

Both intermediate_image_sizes and intermediate_image_sizes_advanced hooks are ok for this task. A super simple example is below, files for my-image-size-name image size won’t be created for images, uploaded for a custom post type page.

add_filter( 'intermediate_image_sizes_advanced', function( $sizes ){

	$post_id = isset( $_REQUEST[ 'post_id' ] ) ? $_REQUEST[ 'post_id' ] : null;
	if( ! $post_id ) {
		return $sizes;
	}
	
	if( 'page' === get_post_type( $post_id ) ) {
		unset( $sizes[ 'my-image-size-name' ] );
	}
 
	return $sizes;
 
} );

A little bit more complicated example, but it is also correct:

add_filter( 'intermediate_image_sizes', function( $sizes ){
	// $sizes - all the image sizes in an array
	// Array ( [0] => thumbnail [1] => medium [2] => large [3] => post-thumbnail )
	
	$post_id = isset( $_REQUEST[ 'post_id' ] ) ? $_REQUEST[ 'post_id' ] : null;
	if( ! $post_id ) {
		return $sizes;
	}
	
	$post_type = get_post_type( $post_id );
 
	foreach( $sizes as $key => $value ) {

		switch( $post_type ) {
			case 'regionfeatured' : {
				unset( $sizes[ $key ] );
				break;
			}
			case 'region' : {
				if( ! in_array( $value, array( 'regionfeatured', 'misha335' ) ) ) {
					unset( $sizes[ $key ] );
				}
				break;
			}
			default : {
				// turn off everything except thumbnail
				if( 'thumbnail' !== $value ){
    				unset( $sizes[$key] );
    			}
				break;	
			}
		}
		
	}
	return $sizes;
}

Removing Image Sizes

Of course in some cases you don’t need so many image files. For example this website don’t even use a single one!

So, how to remove them?

First of all you can set to 0 all the image sizes in settings, like this:

remove default image sizes in WordPress

Or you can use intermediate_image_sizes filter hook. Or remove_image_size() function inside after_setup_theme hook, just like the way we registered them.

add_filter( 'intermediate_image_sizes', 'misha_turn_off_default_sizes' );
 
function misha_turn_off_default_sizes( $sizes ) {
 
	unset( $sizes[ 'thumbnail' ] );
	unset( $sizes[ 'medium' ] );
	unset( $sizes[ 'large' ] );
	unset( $sizes[ 'medium_large' ] ); // remove medium_large image size
	unset( $sizes[ '1536x1536' ] ); // remove 1536x1536 image size
	unset( $sizes[ '2048x2048' ] ); // remove 2048x2048 image size
	
	return $sizes;
 
}

For images with -scaled suffix the approach is a little bit different.

// remove -scaled image sizes
add_filter( 'big_image_size_threshold', '__return_false' );
Misha Rudrastyh

Misha Rudrastyh

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