Output additional WP media sizes

Put this code in a template to see additional sizes:

<?php
global $_wp_additional_image_sizes;
var_dump( $_wp_additional_image_sizes );
?>

Output example:

array (size=8)
  'gallery-slider' => 
    array (size=3)
      'width' => int 300
      'height' => int 200
      'crop' => boolean true
  'square' => 
    array (size=3)
      'width' => int 550
      'height' => int 550
      'crop' => boolean true
  'landscape' => 
    array (size=3)
      'width' => int 800
      'height' => int 600
      'crop' => boolean true
  'portrait' => 
    array (size=3)
      'width' => int 600
      'height' => int 800
      'crop' => boolean true
  'large_width' => 
    array (size=3)
      'width' => int 1000
      'height' => int 500
      'crop' => boolean true
  'large_height' => 
    array (size=3)
      'width' => int 500
      'height' => int 1000
      'crop' => boolean true
  'large_width_height' => 
    array (size=3)
      'width' => int 1000
      'height' => int 1000
      'crop' => boolean true
  'gallery' => 
    array (size=3)
      'width' => int 580
      'height' => int 387
      'crop' => boolean true