What Is Projector Throw Distance?
The throw distance is how far a projector must sit from the screen to produce an image of a given width. Every projector has a throw ratio — the ratio of its distance to the projected image width — printed in its specifications (for example, 1.5:1 means it needs 1.5 units of distance for every 1 unit of image width). This calculator multiplies that throw ratio by your desired screen width to tell you exactly where to position the unit.
How to Use It
Enter your projector's throw ratio (use the single number, e.g. 1.5 for a 1.5:1 lens) and the width of the image or screen you want, in inches. The calculator returns the required throw distance in inches, feet, and meters. If your projector lists a throw ratio range (e.g. 1.2–1.6), run it twice to get the minimum and maximum placement distances.
The Formula Explained
The relationship is simple and linear: $$\text{Throw Distance} = \text{Throw Ratio} \times \text{Screen Width}$$. Because it is linear, doubling the screen width doubles the required distance. Note that throw ratio is based on image width, not the diagonal — if you only know the diagonal of a 16:9 screen, width \(\approx\) diagonal \(\times\) 0.872.
Worked Example
Suppose you have a projector with a 1.5:1 throw ratio and want an 80-inch-wide image. $$\text{Throw Distance} = 1.5 \times 80 = 120 \text{ inches}$$ which is 10 feet or about 3.05 meters. So place the projector roughly 10 feet from the screen.
FAQ
What if my projector has a short-throw lens? Short-throw projectors have ratios below 1.0 (e.g. 0.5), so they sit much closer; ultra-short-throw ratios are around 0.25 or less.
Should I use width or diagonal? Always use the screen width. Throw ratio specifications are defined relative to image width.
Does zoom affect this? Yes — zoom lenses give a range of throw ratios. Use the low end for the nearest placement and the high end for the farthest.
