Get top items number from wordpress menu

by

You can use the wp_get_nav_menu_object to retrieve the menu as an object, which you can subsequently establish the length of. Like this:

$wpse140949_menu = wp_get_nav_menu_object( 'your-menu-name-or-slug' );
$tabcount = $wpse140949_menu->count;

You can the use this on your call to wp_nav_menu:

wp_nav_menu ( array (
  'menu_class' => 'item-' . $tabcount,
  ....
  ));