Correct way of getting the total number of posts is:
<?php $count = $custom_posts->found_posts; ?>
http://codex.wordpress.org/Class_Reference/WP_Query#Properties
Edit: acknowledging @Kresimir Pendic’s answer as probably correct. post_count is the count of posts for that particular page, while found_posts is the count for all available posts that meets the requirements of the query without pagination. Thank you for the correction.