Ideal Projector Distance Calculation
For a 1.5:1 throw ratio and 10 foot diagonal 120-inch screen, multiply ratio by diagonal to get 15 feet optimal throw distance.
Projectors with short throw ratios need less distance for large images. A 1.2-1.5:1 ratio means 1.2-1.5 x image width equals throw distance.
For a 120 inch wide screen, throw ratio x width gives expected distance. 0.47 x 120 inches equals 56.4 inch or 4.7 foot optimal distance. Short throw projectors need 5-10 feet distance depending on image size. Throw ratio ranges 0.38 to 0.65 for short throw.
Viewing Distance Guidelines
Seating distance for 120-inch screen is 10-12 feet. Minimum distance for 120-inch screen is 161 inches; maximum is 227 inches. For 100-inch screen, optimal viewing distance is 119 inches calculated by dividing diagonal screen size by 0.84.
Projection Setup and Environment
Projectors should be 1.5 times screen width from screen. Basements suit projectors being dark. Blackout curtains allow projectors in rooms with windows. 120-inch 16:9 screen dimensions are 104.6 inches wide by 58.8 inches high.