What exactly is this rule? From what I understand if you have a 100" diagonal, you must watch your screen at 160" disctance. Am I correct?

Thanks

In a nutshell, yes. Personal preference allows for considerable variation on this rule. The obvious thing you don't want is to sit so close that your eyes can resolve the individual projected pixels on the screen.

Thank you, Durachko.

Is that rule for diagonal or widths. I would think that viewing distance is dependent on the width of the screen and not the diagonal. The object is to keep from having to turn your head back and forth to watch a movie.

In reference to the width. So a 10ft wide screen should put you back atleast at 16ft.

My understanding of screen size to viewing distance is that the height of the screen should be approximately 1/3 of the viewing distance. If you have a 100" 16x9 screen, the height would be about 49". That would put your viewing distance at around 150".

This is what I am using for determining my screen size. My viewing distance is about 124" so my screen height is at about 44", just what a standard bolt of cloth's width is!