Facebook page owners who want to know how many subscribers they have following their posts without Liking the page can see a list through a little known feature on Timeline.
From the “admin panel” at the top of a page, page owners can see who has recently Liked their page. Clicking “see all” brings up a window that allows admins to also see their subscribers. This is also accessible from the “See Likes” link on the Likes section of page insights. Page owners can tally their subscribers and click on profiles to see more information about who’s following them. It’s unclear when Facebook added this option, but there is no documentation of it in Help Center.[Update 8/15/12 4:58 p.m. PT - Page owners can also now see their total number of subscribers in the “Overview” section of page insights, next to Total Likes, Friends of Fans, People Talking About This and Weekly Total Reach. They do not have to manually count them in the module described above.]
After rolling out Timeline for pages, Facebook began giving users the option to add pages to an interest list to subscribe to content without Liking the page. This feature was hidden in a drop-down menu until last month when some users began seeing a “subscribe” button next to the Like button. However, Facebook did not make it clear to page owners how they could track how many subscribers they have. There still isn’t a way for admins to see which interest lists they are included on, though Facebook gave this option to personal profiles in June.
There is also no data about page subscribers available through the Insights API, though this might be because the percentage of people who subscribe to a page without Liking it is still quite low.