Change Default Thumbnail Size in WordPress

WordPress 2.5 and later include a built-in option to change the size of thumbnails, but for those of you out there using an older version, it is quiet easy to change. It just requires modification of one WordPress file. When WordPress 2.1 was released, it changed the way this was done, and once again with the release of WordPress 2.3, so I have included instructions below for multiple versions.

Instructions for:

• WordPress 2.0
• WordPress 2.1 – 2.2
• WordPress 2.3
• WordPress 2.5 and later

  If you have found this page useful, please consider donating. Thanks!

WordPress 2.0

Open /wp-admin/inline-uploading.php and look for the following code:

if ( $imagedata['width'] > 128 && 
$imagedata['width'] >= $imagedata['height'] * 4 / 3 )
      $thumb = wp_create_thumbnail($file, 128);
    elseif ( $imagedata['height'] > 96 )
      $thumb = wp_create_thumbnail($file, 96);

The default max size is 128 x 96. You can change these numbers to whatever you like, although you must keep the proper aspect ratio (4 / 3).

For example, to double the size of the thumbnails, replace 128 with 256, and 96 with 192. Be sure to change both sets of numbers – they are each listed in the code twice.

WordPress 2.1 – 2.2

Open /wp-admin/admin-functions.php and look for the following code:

$max_side = apply_filters( 'wp_thumbnail_max_side_length', 
128, $attachment_id, $file );

The number specified here (128 by default) is the maximum size of either dimension. Just change this to whatever you like.

WordPress 2.3

Open /wp-admin/includes/image.php and look for the following code:

$max_side = apply_filters( 'wp_thumbnail_max_side_length', 
128, $attachment_id, $file );

The number specified here (128 by default) is the maximum size of either dimension. Just change this to whatever you like.

WordPress 2.5 and later

Version 2.5 and later have built-in support for the thumbnail size in the options.

  If you have found this page useful, please consider donating. Thanks!