Add Meta Boxes to Multiple Post Types

October 16, 2014

add_action( 'add_meta_boxes', 'my_add_custom_box' );
  function my_add_custom_box($postType) {
 	$types = array('type1', 'type2', 'type3');
 	if(in_array($postType, $types)){
 		add_meta_box(
 				'myid',
 				__( 'Title', 'myplugin_textdomain' ),
 				'callback',
 				$postType
 		);
 	} }

Sourced here.