This is where you'll need to measure carefully, because it'll depend on the seats you choose and how much space there is in the room. You generally want to leave a minimum of 20" on the ends of each row, and consider how far seats will recline if you're going to have more than one row (or are trying to fit them into a smaller home theater room). Retailers of home theater seating are usually very happy to provide assistance with measurement guides and even help over the phone, so that you get the perfect setup for your home theater.