Projector Throw Distance Calculator
How far the projector must be from the screen for a given image size and throw ratio, and the largest picture your room allows.
Results
What this tool does
A projector's throw ratio is the distance to the screen divided by the width of the picture, so a 1.5 ratio needs 1.5 m of distance for every metre of width. The catch is that screens are sold by diagonal: a 100-inch 16:9 picture is about 2.21 m wide, so that projector has to sit about 3.3 m away, measured from the lens, not the back of the case. Zoom lenses give a range of ratios, printed as two numbers in the manual; work out both ends. Short-throw models run around 0.4 to 1, ultra-short-throw ones below 0.4, and lens shift or keystone correction does not change the distance, only where the picture lands.
Formula
distance = throw ratio × image width · width = diagonal × k ÷ √(k² + 1)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
tr | Throw ratio of the projector | — |
dg | Screen diagonal | in |
ar | Aspect ratio | — |
rd | Distance available in your room | m |
D | Distance from lens to screen | m |
W | Image width | m |
H | Image height | m |
MD | Largest diagonal from your room distance | in |
Worked example
- Throw ratio of the projector1.5
- Screen diagonal100 in
- Aspect ratio169
- Distance available in your room4 m
- Distance from lens to screen3.32 m
- Image width2.21 m
- Image height1.25 m
- Largest diagonal from your room distance120 in
Limitations
- Coverage and consumption figures vary between products. Take the values from the manufacturer's datasheet for the product you are actually using.