Throw ratio = lens-to-screen distance ÷ image width. Choose which value you need, enter a positive throw ratio and the known distance or image width in the same unit. The result is a planning estimate; always verify the exact projector's manufacturer throw chart, zoom range, offset, lens shift and installation tolerances before purchase or mounting.
Calculate distance, image width or throw ratio
Use image width—not diagonal—and one consistent unit. Final placement must use the exact projector manufacturer's documentation.
Use one unit and the visible formula
| Find | Formula | Inputs |
|---|---|---|
| Distance | throw ratio × image width | Ratio and image width in metres or feet |
| Image width | distance ÷ throw ratio | Lens-to-screen distance and ratio |
| Throw ratio | distance ÷ image width | Measured distance and image width |
What this calculator deliberately does not claim
The result uses ideal straight-line geometry. It does not account for zoom limits, lens shift, offset, cabinet depth, focus tolerance, keystone, ultra-short-throw optics, screen curvature or mounting error.
Use image width—not diagonal—in the formula. If you only know diagonal, first convert it using the intended aspect ratio, then verify the actual screen and projector documentation.
Sources and further reading
Technical statements were reviewed against these references. External pages may change after our review date.
- ISO/IEC 21118:2020 — Information for Data Projector Specification Sheets — International Organization for Standardization
- How to Choose the Right Projector Brightness and Lumens for Your Room — BenQ India