I won’t define this here as we at Projector Reviews.com have already done so in depth via This Article. What I will do is simplify the idea and stress the impact of not taking it into account. Essentially, you want to ensure that the font on the projector screen is equivalently capable of being read as compared to one’s computer screen. More tactically, if you can read 11-point type on a 21-inch display from 28 inches, then for any sized room and seating distance, you want that same level of legibility (or as close to it as possible).
If you are sitting 4 times the 28 inches away (112 inches or 9.3 feet), then your display should be 4 times the height and have a width of a 21 inch – 84-inch diagonal. In larger rooms, that calls for some pretty big displays as the seating distance is conference rooms can be up to 20’ which is far more that the 9-foot example provided above. Gone are the days of 26+ sized font and exclusively PowerPoint. Users want to collaborate over google docs, sheets, Jira and a plethora of tools that require smaller font. A projector is of no use if no one can read it or if you must zoom in to 200% and crop out half the screen in doing so. To keep it easy, reference the table below for best practices.