What is my projector throw distance?
Type your projector’s throw ratio from its specs and the image size you want. The calculator gives the distance from the lens to the screen, and the range of distances for a zoom lens.
- Throw distance
- 10.89 ft
A 100 in image at a throw ratio of 1.5 needs a throw distance of 10.89 ft.
- Image width
- 87.16 in
- Image height
- 49.03 in
Throw distance: 10.89 ft. A 100 in image at a throw ratio of 1.5 needs a throw distance of 10.89 ft.
How to calculate
Works out how far a projector must sit from the screen for a given image size, from its throw ratio and the aspect ratio, with the range for a zoom lens.
Example with the default inputs (Throw ratio 1.5, Image size (diagonal) 100 in, Image aspect ratio 16:9): A 100 in image at a throw ratio of 1.5 needs a throw distance of 10.89 ft.
Method: Throw distance = throw ratio × image width; image width = diagonal × a ÷ √(a² + b²) for an aspect ratio a : b.
- The distance is from the projector’s lens to the screen, with the projector square to the screen.
- The throw ratio is the maker’s figure for the image width; keystone or digital zoom changes the picture size.
Worked examples
Each example is checked against the calculator on every build.
- Throw ratio 1.5, Image size (diagonal) 100 in, Image aspect ratio 16:9 gives Image width 87.16 in, Throw distance 10.89 ft.Source: Throw (projector), Wikipedia (throw ratio = distance from the lens to the screen ÷ screen width), https://en.wikipedia.org/wiki/Throw_(projector) (retrieved 2026-10-03)
- Throw ratio 2, Image size (diagonal) 75 in, Image aspect ratio 4:3 gives Image width 60 in, Image height 45 in, Throw distance 10 ft.Source: Throw (projector), Wikipedia (throw ratio = distance from the lens to the screen ÷ screen width), https://en.wikipedia.org/wiki/Throw_(projector) (retrieved 2026-10-03) (a 2.0 ratio puts a 60 in wide image 120 in away)
- Throw ratio 1.36, Throw ratio, long end of zoom 2.18, Image size (diagonal) 118.1 in, Image aspect ratio 16:9 gives Throw distance 11.67 ft, Throw distance, long end of zoom 18.7 ft.Source: Throw (projector), Wikipedia (throw ratio = distance from the lens to the screen ÷ screen width), https://en.wikipedia.org/wiki/Throw_(projector) (retrieved 2026-10-03)
How it works
- Image width from the diagonal d and the aspect ratio a : b (Pythagoras): W = d × a ÷ √(a² + b²), and height H = d × b ÷ √(a² + b²).
- Throw distance = throw ratio × W.
- With a zoom lens, the long-end ratio gives the longest distance the same way.
The listed aspect ratios are 16:9, 16:10, 21:9, 4:3 and 2.39:1, each exactly as written; with Other you type the two parts (0.01 to 1,000).
Rules
- The throw ratio is 0.05 to 20. The long-end ratio is optional; when it is smaller than the throw ratio, there is no answer.
- The image diagonal is 1 in to 2,000 in, in inches or centimeters, used as the exact decimal typed.
- The distance shows in feet in US units and meters in Metric; the width and height in inches or centimeters.
Worked examples by hand
100 in at 16:9, ratio 1.5. √(16² + 9²) = √337 = 18.358. W = 100 × 16 ÷ 18.358 = 87.16 in. Distance 1.5 × 87.16 = 130.7 in = 10.89 ft.
75 in at 4:3, ratio 2.0. √(4² + 3²) = 5. W = 75 × 4 ÷ 5 = 60 in; H = 45 in. Distance 2 × 60 = 120 in = 10 ft.
300 cm at 16:9, zoom 1.36 to 2.18. W = 300 × 16 ÷ 18.358 = 261.47 cm. Distance 355.6 cm at 1.36 and 570.0 cm at 2.18.
Other questions people ask
What is a throw ratio?
The distance from the projector’s lens to the screen divided by the width of the image. A 1.5 ratio means the projector sits 1.5 ft back for every foot of image width.
How do I calculate throw distance?
Multiply the throw ratio by the image width. For a 100 in 16:9 image, the width is 100 × 16 ÷ √(16² + 9²) = 87.2 in, so at a 1.5 ratio the lens sits 130.7 in (10.9 ft) from the screen.
What does a zoom range such as 1.36 to 2.18 mean?
The zoom lens can give any throw ratio in that range, so the projector can sit anywhere between the short and the long distance for the same image size. Type both numbers to see the range.
What is a short-throw projector?
One with a throw ratio below about 1, so it makes a large image from close up. Ultra-short-throw models are below about 0.4 and sit just in front of the wall.
Where do I measure the distance from?
From the front of the lens to the screen. Makers’ distance tables use the lens; add the depth of the projector behind it when you plan a shelf or a mount.