Formula and method
throw distance = image width × throw ratio
Projector throw ratio is based on image width, not diagonal. The screen dimensions first come from diagonal and aspect ratio, then the selected throw ratio determines lens distance.
Assumptions and limits
- Throw distance is measured from the projector lens to the screen.
- Lens shift, zoom range and installation tolerances must be checked in the projector manual.
- The calculator does not include overscan or keystone correction.
Worked examples
100-inch 16:9 screen at 1.5 throw ratio
The image is 87.16 inches wide. The lens should be about 130.73 inches, or 3.32 m, from the screen.
120-inch 16:10 screen at 1.2 ratio
The image width is about 101.76 inches, giving a throw distance of roughly 122.11 inches or 3.10 m.
Common 16:9 projector screens
| Diagonal | Image width | Image height |
|---|---|---|
| 80 in | 69.73 in / 1.77 m | 39.22 in / 1.00 m |
| 100 in | 87.16 in / 2.21 m | 49.03 in / 1.25 m |
| 120 in | 104.59 in / 2.66 m | 58.84 in / 1.49 m |
Frequently asked questions
Is throw ratio based on screen width or diagonal?
It is based on image width. Using diagonal would place the projector incorrectly.
Can this replace the manufacturer’s calculator?
No. Use it for planning, then verify the exact zoom, lens shift and mounting range in the manufacturer documentation.