In order to determine the best size screen, one must determine their aspect ratio. An apsect ratio of: 1:1 was primarily for slide projectors and overhead projectors. I bet many of you reading this right now have never even seen one of these projectors in person. 4:3 aspect ratio is primarily used for non-HD television and Video format media. This too has become less common as more widescreen formats are becoming widely adopted. 16:9 is the current standard today for DVD and High Definition Content. 16:10 is the most common format for data applications, such as presentations and other content from a modern computer. 2.35:1 format is far more specialized. This is the cinematic format used in major motion picture production and is what you experience in the movie theater. A 100" diagonal 16:9 format screen has a viewable width of 87". In 4:3 format that width would be 80" and in 2.35:1 format the width would be 92". Once you have determined the aspect ratio which you plan on using you can apply this simple formula (as a rule of thumb): Room Depth / 2 = Your Screen's Diagonal Size For example: If the room is 20 ft deep/long, the screen diagonal should be 10 ft. Other factors play into the ideal screen size for any application such as the rooms seating configuration and the projector mounting location. The above is general rule of thumb for determining screen size only. If you need any assistance in determining the optimal screen size, aspect ratio or anything else make sure to contact us; we are here to help!