How to use it
- Choose what to find: the distance for a screen you have, or the picture size from where the projector can go.
- Pick metric or feet and inches, enter the throw ratio from the projector’s specifications and choose the aspect ratio of the picture.
- Enter the screen diagonal in inches (as screens are sold) or the distance from the lens.
- Read the distance or the diagonal, with the picture width and height.
The formulas
For an aspect ratio a : b, the diagonal d gives
width = d × a ÷ √(a² + b²), height = width × b ÷ a
throw distance = throw ratio × width, and the other way width = distance ÷ throw ratio.
The distance is measured from the front of the lens; check the manual, as some makers measure from another point of the body.
Worked example
A 100-inch 16:9 screen with a 1.5 : 1 projector:
- √(16² + 9²) = 18.358, so the width is 100 × 16 ÷ 18.358 = 87.16 in = 221.4 cm and the height 49.03 in = 124.5 cm;
- distance = 1.5 × 221.4 cm = 3.32 m, or 10.89 ft.
The other way: 3 m from the screen with the same projector, the picture is 3 ÷ 1.5 = 2 m wide, 112.5 cm high and 90.3 inches on the diagonal.
Tips
- Measure the distance to the screen surface, not to the wall behind it if the screen hangs in front.
- Leave room behind the projector for cables and air vents.
- For a 4:3 picture on a 16:9 screen, enter the diagonal of the 4:3 area you want to fill.