How do I calculate projector distance from a screen?

Multiply your image width by the lens throw ratio. A 4 metre wide image on a 1.5:1 lens needs 6 metres of throw distance. With a zoom lens you get a usable range rather than a single figure.

What is a short throw projector?

A short throw projector uses a lens with a throw ratio of roughly 0.4:1 or less, producing a large image from very close to the screen. They suit rear projection with limited depth behind the screen, and wall mounted setups.

How many lumens do I need?

It depends on screen area and ambient light. A blackout room needs far fewer lumens per square metre than a daylit hall. Screen brightness is measured in foot-lamberts: roughly 12 to 22 fL for a dark room, 25 to 50 fL for a typical dimmed event, and more where there is significant ambient light.

Projector Throw Distance Calculator – iTRINITY

1. Choose the projector or lens

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Model / lens

Throw ratio — wide & tele

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Projector brightness (optional) Fill this in to get screen brightness in foot-lamberts

2. Screen & room

Units

What do you already know?

Enter size as

Screen diagonal m

4.59 m

Aspect ratio

Screen gain Matte white is 1.0. Check your screen's spec.

Ambient light

Throw distance—

Image width—

Image height—

Diagonal—

Throw ratio—

Screen area—

Lumens needed—

Reading the diagram. Throw distance runs from the lens to the screen surface. A zoom lens gives a range of valid positions — anywhere inside the dashed band works. The dotted line is the lens centre; where a lens offset is set, the image sits above or below it. Brightness figures assume an even, unobstructed screen — always confirm against the lens and projector spec sheets before ordering.

Projection Basics

How Throw Distance Works

What is throw distance?

Throw distance is simply the gap between the projector lens and the surface you are projecting onto. It is the single measurement that decides how big your image will be — move the projector back and the image grows, move it forward and it shrinks.

What is a throw ratio?

Throw ratio is throw distance divided by image width. A 2.0:1 lens needs two metres of distance for every one metre of image width, so a 5 m wide image needs 10 m of room. Because the relationship is a straight multiplication, once you know the throw ratio you can work out either figure from the other. A zoom lens quotes two ratios — one at full wide, one at full tele — and anything between them is achievable.

How do I work out where to put the projector?

Multiply your intended image width by the throw ratio. A 4 m wide screen on a 1.5:1 lens puts the projector 6 m back. If the lens zooms from 1.3 to 1.8, the same screen can be lit from anywhere between 5.2 m and 7.2 m — useful when a truss position or a doorway is fixed and you cannot move it.

What counts as short throw?

Roughly 0.4:1 or lower. These lenses fill a big screen from very close, which matters for rear projection where there is little depth behind the screen, or for wall-mounted installs where people would otherwise walk through the beam. Ultra short throw lenses go further still and sit almost against the surface.

What is lens shift, and why does it matter?

Lens shift moves the image up, down or sideways without tilting the projector. It is quoted as a percentage of image height. Using shift rather than tilting keeps the image rectangular — tilting forces you into keystone correction, which throws away pixels and softens the picture. On a rigged show, shift is what lets you fly a projector above head height and still hit the screen squarely.

How bright does the image need to be?

Brightness on the screen is measured in foot-lamberts, and it depends on the projector's lumens, the screen's gain and — crucially — the screen's area. Doubling the image width quadruples the area, so brightness falls fast as you scale up. As a working guide: about 12–22 fL suits a blacked-out room, 25–50 fL a typical dimmed event, and you need considerably more where daylight or house lights are in play. Enter your projector's lumens above and the calculator will show where you land.

Planning a real job? These numbers get you to the right ballpark. Site conditions — rigging points, ambient light, screen material, audience sightlines — decide the rest. Send us your numbers and we'll sanity-check the whole setup for you.

Want Us to Spec the Whole Room?

Send the numbers above and we'll come back with the right projector, lens, screen and rigging — or run the entire show for you.

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