How far should a projector be from the screen?
Every projector lens has a throw ratio: how far back the projector must be for each unit of image width. Multiply it by the image width you want and you have the distance from the lens to the screen.
Throw distance = throw ratio × image width
Example: a projector with a 1.5 throw ratio and a 2.4 m wide screen needs to sit 1.5 × 2.4 = 3.6 m from the screen.
Zoom lenses give you a range
A zoom lens lists two ratios, for example 1.4–2.2. Run the calculator with both to get the closest and farthest mounting position. For a 2.4 m wide image that is 3.36 m to 5.28 m. Mount near the middle of the range when you can, so there is room to adjust on site.
Before you drill
- Most manufacturers measure throw from the front of the lens. Check the manual, as some measure from the front of the housing.
- Lens shift and offset decide how high or low the projector sits relative to the screen. They don't change the distance.
- Throw ratio is based on image width, not the diagonal. If you only know the diagonal of a 16:9 screen, width = diagonal × 0.872.
Common questions
What is a throw ratio?
It's the distance from the lens to the screen divided by the image width. A 1.5 ratio means 1.5 m back for every 1 m of image width.
What counts as short throw?
Roughly, a throw ratio below 1.0 is short throw and below about 0.4 is ultra short throw. Short throw lenses let you mount close to the screen and reduce shadows from presenters.
Does the aspect ratio change the distance?
No. Distance depends only on throw ratio and image width. The aspect ratio changes the image height and diagonal.
How do I get the image width from a screen size in inches?
For 16:9, multiply the diagonal by 0.872, then by 0.0254 to get metres. A 100" screen is about 2.21 m wide. For 16:10, multiply by 0.848.