Formula and method
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.
120 Inch Projector Screen Throw Distance
A 120 inch 16:9 projector screen has an image width of about 104.59 inches, or 2.66 meters. Multiply that width by the projector throw ratio to estimate lens distance.
At a 1.2 throw ratio, the lens is about 125.51 inches from the screen. At a 1.5 throw ratio, it is about 156.88 inches from the screen.
Projector Throw Ratio Calculator
Throw ratio connects projector placement to image width. The forward calculation is distance = image width x throw ratio.
If you already know the available lens distance, reverse the formula: throw ratio = distance ÷ image width. Always confirm the final range against the specific projector model.
Common 16:9 projector screens and throw distances
| Diagonal | Image width | Image height | Throw at 1.2 | Throw at 1.5 |
|---|---|---|---|---|
| 80 in | 69.73 in / 1.77 m | 39.22 in / 1.00 m | 83.67 in / 2.13 m | 104.59 in / 2.66 m |
| 100 in | 87.16 in / 2.21 m | 49.03 in / 1.25 m | 104.59 in / 2.66 m | 130.74 in / 3.32 m |
| 120 in | 104.59 in / 2.66 m | 58.83 in / 1.49 m | 125.51 in / 3.19 m | 156.88 in / 3.98 m |
| 150 in | 130.74 in / 3.32 m | 73.54 in / 1.87 m | 156.88 in / 3.98 m | 196.10 in / 4.98 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.
What does a 1.2 throw ratio mean?
It means the projector lens should be 1.2 times the image width away from the screen, before accounting for zoom and installation tolerances.
Should I include the screen frame?
No. Use the projected image area, not the outer frame, border or wall mount.
How far back for a 120 inch projector screen?
For a 120 inch 16:9 screen, the image width is about 104.59 inches. At 1.2 throw ratio the lens distance is about 125.51 inches, and at 1.5 it is about 156.88 inches.
Is this also a projector throw ratio calculator?
Yes. If you know the screen width and lens distance, divide distance by image width to estimate throw ratio; if you know throw ratio, this page estimates lens distance.