Projector throw distance calculator
Every projector lens has a throw ratio: the distance to the screen divided by the width of the image. With that figure from the specification sheet and the screen size you want, this calculator gives the distance range; with the distance you have, it gives the image sizes the lens can produce.
Results are estimates for planning. Check the manufacturer's manual before you drill, buy or mount anything.
How it works
Throw ratio is defined as distance ÷ image width, so
distance = throw ratio × image width, image width = diagonal × a / √(a² + 1)
A zoom lens has two throw ratios: the shorter one (wide end) gives the biggest image from a given distance, the longer one (tele end) the smallest. Reading the formula backwards, image width = distance ÷ throw ratio.
Assumptions and limits
- Distance is measured from the front of the lens. Some manufacturers measure from the back of the case; check the manual.
- Throw ratio does not cover vertical position. Lens shift or offset decides how high or low the projector can sit relative to the screen.
- Using the extremes of a zoom range can reduce brightness or sharpness on some lenses.
Sources
Last reviewed: November 2026.