How to use the projector throw distance calculator
- Choose whether to find the distance to the screen or the screen width at a distance.
- Enter the screen width or diagonal with its aspect ratio, or enter the distance you have, and pick the unit.
- Type the throw ratio from the projector manual. Enter a shortest and a longest ratio for a zoom lens, or only the shortest for a fixed lens.
- Read the distance range, the screen width and height, and the distance in feet and meters. Measure from the lens to the screen.
Formula
Throw ratio = distance / screen width
Distance = throw ratio x screen width
Screen width = diagonal x aspect width / sqrt(aspect width^2 + aspect height^2)
Screen height = width x aspect height / aspect width
A zoom lens has a range of throw ratios, so it works across a range of distances for the same screen. A fixed lens has a single ratio and a single distance.
A 100 inch diagonal 16:9 screen
A 16:9 screen with a 100 inch diagonal is 100 x 16 / sqrt(16^2 + 9^2) = 87.16 inches wide and 49.03 inches tall. With a zoom lens that has a throw ratio of 1.15 to 1.5, the projector can sit from 87.16 x 1.15 = 100.23 inches to 87.16 x 1.5 = 130.74 inches from the screen, which is 8.35 to 10.89 feet or 2.55 to 3.32 meters.
For a fixed lens with a throw ratio of 1.6 and a 4:3 screen with a 120 inch diagonal, the screen is 96 by 72 inches and the distance is 153.6 inches, or 12.8 feet. Working backward, a projector 12 feet from the screen with a ratio range of 1.2 to 1.5 fills a screen 8 to 10 feet wide.
What a throw ratio means
The throw ratio is how far back you put the projector for each unit of image width. A ratio of 1.5 means a 100 inch wide image needs 150 inches of distance. Short-throw projectors have ratios well under 1 and sit close to the wall, while standard lenses are around 1.2 to 2. The ratio on a spec sheet is usually given as a range for a zoom lens and sometimes depends on the picture format, so use the figure for your aspect ratio.
If you are starting from a TV size you like, the Screen Dimensions Calculator turns a diagonal into width and height. To choose how far back to sit, use the TV Size and Viewing Distance Calculator.
Setting up the room
Measure from the projector lens to the screen, not from the front of the case. Leave room for the tilt of a ceiling mount, and note that the image rises or falls with lens shift or keystone correction, which can change the effective ratio. Use the lower end of the distance range if the room is short, and test with a temporary setup before drilling. If you work from scaled room plans, the Architectural Scale Calculator converts lengths from the drawing, and the Aspect Ratio Calculator helps with unusual screen shapes.
Assumptions and limits
- The throw ratio is the one you type. The values shown, 1.15 and 1.5, are examples and not a standard for any projector.
- The screen is flat and the projector is centered and level, with no lens shift or keystone correction.
- The aspect ratio of the picture matches the screen.
- All arithmetic happens in your browser and nothing is stored or sent.
Frequently asked questions
How far should a projector be from the screen?
Multiply the screen width by the throw ratio on the spec sheet. A zoom lens gives a shortest and a longest distance. For a screen 87 inches wide and a ratio from 1.15 to 1.5, that is about 100 to 131 inches.
Do I enter the screen width or the diagonal?
Either. Pick the one you know. If you pick the diagonal, choose the aspect ratio so the tool can find the width, since the throw ratio is based on width.
What is the difference between 16:9 and 16:10 here?
For the same diagonal, a 16:10 screen is a little narrower and taller than a 16:9 screen, so the width and the throw distance are a little smaller. Choose the ratio of the screen you have.
Where do I measure the distance from?
Measure from the projector lens to the surface of the screen. Many manuals describe the distance to the front of the lens, so check yours, and allow a few inches for the case.