The best way to find out is to measure (in inches) from where the TV will be wall-mounted or placed on a stand to where you will be sitting, and then divide that measurement by 2. If your couch is anywhere from 150 to 170 inches (12.5 to 14 feet) from the TV, an 85-inch screen will be an almost perfect fit. You can, of course, go a bit bigger (if possible) or smaller depending on what your budget is and what's available from each brand. A screen that is too big can overwhelm your space and even cause motion sickness. while one that is too small will make it feel cavernous and force everyone to crowd around in order to see.