<?php add_filter( 'manage_upload_columns', 'wpse_237131_add_column_file_size' ); add_action( 'manage_media_custom_column', 'wpse_237131_column_file_size', 10, 2 ); function wpse_237131_add_column_file_size( $columns ) { // Create the column $columns['filesize'] = 'File Size'; return $columns; } function wpse_237131_column_file_size( $column_name, $media_item ) { // Display the file size if ( 'filesize' != $column_name || !wp_attachment_is_image( $media_item ) ) { return; } $filesize = filesize( get_attached_file( $media_item ) ); $filesize = size_format($filesize, 2); echo $filesize; }