THX has established a two step process for calculating the best viewing distance for 1080p HDTVs.
Step 1: Measure the diagonal screen size
Step 2: Divide by .84
For example, an HDTV display with a 65-inch screen divided by .84 equals a 77-inch viewing distance (6.5 feet).
The goal is to have a 40° or less viewing angle. This provides the greatest combination of visual impact with sharp detail.
Make sure that each viewer has a clear site line to the display. Take care not to place the display too high on the wall. Viewers should not have to look up more than 15°.
