Custom fields adds some extra meta-data to our posts and pages. We can only display that meta-data inside the loop, not outside.
WordPress stores all the data into its MySQL database, so we will just made a MySQL query to get the custom field value outside the loop of your post. In short, here’s a nice trick to get custom fields outside the loop of your WordPress posts and pages.
Just add following snippet anywhere in your WordPress theme:
$postid = $wp_query->post->ID;
echo get_post_meta($postid, 'CUSTOM-FIELD-NAME', true);
Just replace the CUSTOM-FIELD-NAME in above code with the name of your custom field. That will do the job!