Projector Throw Calculator

This projector throw calculator works out how far your projector needs to be from the screen, based on its throw ratio and the image size you want. It also works in reverse: enter the distance you have available and it shows the image size you will get, including the smallest and largest image a zoom lens can produce.

You can enter a single throw ratio for a fixed lens or a minimum and maximum for a zoom lens, choose the aspect ratio of your screen (16:9, 16:10, 4:3 or 2.35:1), and describe the screen by its diagonal or its width. Units can be inches and feet or centimeters and meters.

How to Use the Projector Throw Calculator

1
Choose a direction
Use the Screen size to distance tab to find where to mount the projector, or the Distance to screen size tab to see what image fits a room.
2
Enter the throw ratio
Type the throw ratio from your projector spec sheet in the min box. For a zoom lens listed as a range, such as 1.36 to 1.64, put the second number in the max box.
3
Set aspect ratio and size or distance
Pick the aspect ratio of your screen, then enter its diagonal or width, or the lens-to-screen distance. Switch on metric units to use centimeters and meters.
4
Read the results
The result shows the throw distance range or the image diagonal, width and height. Confirm the numbers with the maker's own calculator before mounting.

How throw ratio works

A projector's throw ratio is the distance from the lens to the screen divided by the width of the image it makes. A throw ratio of 1.5:1 means that for every foot of image width, the projector sits 1.5 feet away. The ratio is fixed by the lens, so once you know it you can find the distance for any screen width, or the width for any distance.

Screens are usually sold by diagonal, so the calculator first converts the diagonal to a width using the aspect ratio. For a screen with aspect ratio a:b, the width is the diagonal times a divided by the square root of a squared plus b squared. That factor is 0.8716 for 16:9, 0.8480 for 16:10, 0.8 for 4:3 and 0.9202 for 2.35:1.

Throw distance = throw ratio x image width. Image width = diagonal x a / sqrt(a^2 + b^2). Reverse: image width = throw distance / throw ratio

Worked example: a 120-inch 16:9 screen

Say your projector has a zoom lens with a throw ratio of 1.36 to 1.64 and you want a 120-inch diagonal 16:9 image.

Image width: 120 x 0.8716 = 104.6 inches
Shortest distance (widest zoom): 1.36 x 104.6 = 142.2 inches, about 11.9 ft (11 ft 10 in)
Longest distance (full telephoto): 1.64 x 104.6 = 171.5 inches, about 14.3 ft (14 ft 4 in)
Any lens position from about 11.9 to 14.3 feet from the screen will fill the 120-inch screen

Worked example: what fits at 12 feet

Now reverse it. Your room lets you place the same projector 12 feet (144 inches) from the wall. At the widest zoom, 144 / 1.36 = 105.9 inches of image width, which is a 121.5-inch 16:9 diagonal. At full telephoto, 144 / 1.64 = 87.8 inches wide, a 100.7-inch diagonal. So a 100 to 120 inch screen works from that spot.

Throw distance for a 100-inch 16:9 screen

A 100-inch 16:9 screen is 87.2 inches wide and 49 inches tall. The table shows the throw distance for common throw ratios, computed the same way the calculator does.

Throw ratio	Typical lens type	Throw distance
0.25:1	Ultra short throw	1.8 ft (0.55 m)
0.5:1	Short throw	3.6 ft (1.11 m)
0.8:1	Short throw	5.8 ft (1.77 m)
1.2:1	Standard	8.7 ft (2.66 m)
1.5:1	Standard	10.9 ft (3.32 m)
2.0:1	Long throw	14.5 ft (4.43 m)

Tips and common mistakes

Measure from the lens, not the back of the projector. The body can add several inches to a ceiling mount.
Ultra short throw projectors often quote distance from the screen to the back of the unit or give a separate table. Use the maker's figures for those.
Match the aspect ratio to your screen, not the source. A 2.35:1 movie on a 16:9 screen still uses the 16:9 width.
Plan for lens offset. Many projectors throw the image above or below the lens center, which sets the mounting height, and this calculator does not account for it.
Avoid digital keystone correction when you can. It scales the image down and softens detail; physical placement or lens shift is better.

Your projector's manual is the final word

Manufacturers round throw ratios on spec sheets, and lens shift, offset and zoom tolerances vary between models. Treat these results as a planning estimate and check your projector's manual or the manufacturer's online throw calculator before drilling ceiling mount holes or running cables through walls.

Features

Screen size to throw distance, and distance to image size
Fixed throw ratio or min–max zoom range
Enter the screen diagonal or width
16:9, 16:10, 4:3 and 2.35:1 aspect ratios
Imperial (in and ft) or metric (cm and m) units

Frequently Asked Questions

How do you calculate projector throw distance?

Multiply the projector's throw ratio by the width of the image you want. For a 100-inch 16:9 screen, the width is 100 x 0.8716 = 87.2 inches. With a 1.5:1 throw ratio, the throw distance is 1.5 x 87.2 = 130.7 inches, or about 10.9 feet from lens to screen.

What does a throw ratio of 1.5:1 mean?

It means the projector must sit 1.5 units away for every 1 unit of image width. To make an image 8 feet wide, the lens needs to be 12 feet from the screen. A lower number means a shorter throw: a 0.5:1 short-throw projector makes the same 8-foot-wide image from just 4 feet away.

How far should a projector be from a 120-inch screen?

It depends on the throw ratio. A 120-inch 16:9 screen is 104.6 inches wide. At a 1.2:1 throw ratio the lens goes about 10.5 feet away, at 1.5:1 about 13.1 feet, and at 2.0:1 about 17.4 feet. With a zoom lens you get a range of distances rather than one fixed spot.

What is a short throw projector?

Short throw projectors typically have a throw ratio below about 1:1, often around 0.4 to 0.8, so they make a large image from a few feet away. Ultra short throw models go down to roughly 0.25 to 0.4 and sit just inches from the wall. They suit small rooms and reduce shadows from people walking in front of the beam.

Why does my image not match the calculated size exactly?

Spec sheets round throw ratios, and zoom lenses have tolerances. Measuring from the wrong point, such as the back of the projector instead of the lens, also causes errors. Keystone correction shrinks the image as well. Use this result to get close, then fine-tune with the zoom and check the manufacturer's own throw calculator.

Last reviewed September 21, 2026