How do you calculate the best seat-to-screen distance for a TV or projection screen? Divide the size of your screen by .84 (screen size is measured diagonally). For example, a 65-inch TV divided by .84 equals a 77-inch viewing distance (6.5 feet).
If your HDTV is going in a living room with limited space, THX recommends the following:
It might seem that THX is recommending a very large screen size for your room. But, it’s important to note two things: 1) THX screen size recommendations are based on recreating an immersive cinematic experience, and 2) the biggest complaint among TV buyers is that they wish they had bought a bigger set.
Make sure each seating position in your home theater has a clear site line to the screen. Try not to place the screen too high on the wall – viewers should not have to look up more than 15°.