About the Projector Throw Distance Calculator
This projector throw distance calculator tells you where to put a projector for the screen you want, or how big the image will be from where the projector has to sit. It uses the throw ratio printed in every projector’s specifications — the distance from the lens to the screen divided by the width of the picture.
It is useful when planning a home theater, mounting a ceiling projector, choosing between a standard and a short-throw model, or checking whether a projector will fill your screen in a small room. Choose the aspect ratio of your screen (16:9 for most home projectors and TV content, 16:10 for many business projectors, 4:3 for older models, 2.35:1 for cinemascope screens) and work in inches and feet or in centimetres and metres.
Distances are measured from the front of the lens. For zoom lenses, run the calculation at both ends of the throw ratio range to get the closest and farthest positions. Lens shift and keystone correction do not change the throw distance, but keystone does shrink the usable image.
How to use the projector throw distance calculator
- 1Find the throw ratio in your projector’s specifications (e.g. 1.50:1 → 1.5).
- 2Choose whether you know the screen size or the distance.
- 3Select your units and the screen aspect ratio.
- 4Enter the screen diagonal or the lens-to-screen distance.
- 5Read the result, and use the table to compare common screen sizes.
Formula and method
Throw ratio is defined as the throw distance divided by the image width, so the distance is simply the throw ratio times the width. Screens are sold by diagonal, so the calculator first converts the diagonal into width and height with the Pythagorean theorem and the aspect ratio: for 16:9, the width is 16 ÷ √(16² + 9²) ≈ 0.872 of the diagonal.
To find the screen size from a distance, it reverses the steps: width = distance ÷ throw ratio, then diagonal = width × √(a² + b²) ÷ a. Distances are from the front of the lens to the screen surface, and assume the projector is square to the screen with no digital zoom or keystone applied.
- T
- Throw ratio (distance ÷ image width)
- D
- Image diagonal
- W
- Image width
- a:b
- Aspect ratio, width to height (e.g. 16:9)
Worked examples
100" 16:9 screen with a 1.5 throw ratio
A 100-inch 16:9 picture is 100 × 16 ÷ √337 = 87.16 inches wide. Multiplying by the 1.5 throw ratio gives 130.7 inches, or about 10.9 feet (10 ft 11 in) from lens to screen.
Screen size from 12 ft with a 1.2 throw ratio
From 144 inches away, a 1.2 throw ratio projects an image 144 ÷ 1.2 = 120 inches wide. At 16:9 that is 67.5 inches tall and about 137.7 inches diagonal.
Short-throw projector, 254 cm (100") screen
A 254 cm 16:9 screen is 221.4 cm wide. With a 0.5 short-throw ratio the lens needs to be only 0.5 × 221.4 = 110.7 cm, about 1.11 m, from the screen.
Frequently asked questions
What is a projector throw ratio?+
Throw ratio is the distance from the lens to the screen divided by the width of the image. A ratio of 1.5:1 means the projector must be 1.5 feet back for every foot of picture width.
How far should a projector be from a 100-inch screen?+
For a 16:9 100-inch screen the image is about 87 inches wide, so a 1.5 throw ratio projector needs roughly 10.9 feet, a 1.2 ratio about 8.7 feet and a 0.5 short-throw only about 3.6 feet.
What counts as a short-throw projector?+
Projectors with a throw ratio below about 1.0 are usually called short-throw, and ultra-short-throw models are often under 0.4, sitting just inches from the wall. Standard home projectors are typically 1.2 to 2.0.
How do zoom lenses affect throw distance?+
A zoom lens has a throw ratio range, such as 1.4–1.8. Run the calculation at both ends: the low ratio gives the closest placement and the high ratio the farthest for the same screen size.
Does keystone correction change the throw distance?+
No. Keystone correction digitally reshapes the image to fix angled projection, which slightly shrinks the usable picture and reduces sharpness. Lens shift moves the image without that loss, but neither changes the throw ratio.