How to use this calculator
Enter the screen diagonal size, choose the aspect ratio, and enter the projector throw ratio from the product specifications. If your projector lists a throw ratio range, enter the lower number as the minimum and the higher number as the maximum.
The result is the estimated lens-to-screen distance. Measure from the projector lens, not from the back of the projector or the wall. Leave extra room for the projector body, mount, power cable, and HDMI cable bend radius.
If you know your room depth but not your screen size, the planned Projector Screen Size Calculator will solve the reverse problem in this category.
Projector throw distance formula
image width = diagonal x aspect width / sqrt(aspect width^2 + aspect height^2)throw distance = image width x throw ratioThrow ratio is based on image width, not diagonal size. The calculator first converts diagonal screen size into image width, then multiplies that width by the throw ratio range.
Assumptions and methodology
This calculator estimates optical throw distance from screen geometry and projector throw ratio. It does not calculate vertical offset, lens shift, keystone correction, ceiling mount drop, or whether the image will clear furniture.
- Screen size is treated as visible image diagonal.
- Distance is measured from projector lens to screen surface.
- A throw ratio range usually means the projector has optical zoom.
- Always check the manufacturer manual before drilling or mounting.
A good planning estimate starts with the lens-to-screen number, then separately checks the projector body depth, mount plate, cable clearance, vertical offset, and lens shift range. Treat the result as the optical distance, not the final screw position on a ceiling or shelf.
Example calculations
120-inch 16:9 screen, 1.2-1.5:1 throw ratio
A 120-inch 16:9 screen is about 105 inches wide. With a 1.2-1.5:1 throw ratio, the projector lens should be about 10.5 to 13.1 feet from the screen, or 3.19 to 3.98 meters.
Projector throw distance chart
This chart assumes a 16:9 screen and a 1.2-1.5:1 throw ratio. Use the calculator above for your exact screen size and projector specs.
| Screen size | Image width | Distance | Metric |
|---|---|---|---|
| 80 in | 69.7 in | 6.97-8.72 ft | 2.13-2.66 m |
| 100 in | 87.2 in | 8.72-10.9 ft | 2.66-3.32 m |
| 120 in | 105 in | 10.5-13.1 ft | 3.19-3.98 m |
| 150 in | 131 in | 13.1-16.3 ft | 3.98-4.98 m |
Popular projector distance questions
These quick answer pages cover common setup questions, such as how far back a projector should be for 100, 120, or 150 inches, and how short throw or ultra short throw placement changes the room plan.
Related calculators
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Projector Mount Distance Calculator
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FAQ
How do I calculate projector throw distance?
Multiply the image width by the projector throw ratio. For example, a 100-inch-wide image with a 1.2:1 throw ratio needs about 120 inches of lens-to-screen distance.
Is throw distance measured from the wall or the lens?
Throw distance is measured from the projector lens to the screen surface. The projector body, mount plate, cables, and wall clearance can add extra physical depth.
What does a 1.2-1.5:1 throw ratio mean?
It means the projector can sit about 1.2 to 1.5 times the image width away from the screen. The range usually comes from optical zoom.
Can I use this for short throw or ultra short throw projectors?
Yes, if you enter the correct throw ratio. Ultra short throw projectors often have very low throw ratios, but they also require careful cabinet height, screen type, and wall alignment.
Does lens shift change throw distance?
No. Lens shift changes the image position up, down, left, or right. Throw distance is still based on image width and throw ratio.
Why does the calculator use screen width instead of diagonal size?
Throw ratio is defined against image width. The calculator converts diagonal screen size into width using the selected aspect ratio, then applies the throw ratio.