Projector screen size calculator
A projector is quoted by its throw ratio: the distance from the lens to the wall, divided by the width of the picture it makes there. Give it that and one measurement, and this gives you the other — drawn on the wall at true scale.
On the projector's spec sheet — distance divided by image width. A short-throw is under 1.
- Image
- 233.3 cm × 131.3 cma 105 inch picture
- From
- 3.5 mat a throw ratio of 1.5:1
- Sit
- 3.2 m – 3.8 mfor films, by the same band the TV tool scores against
A projected image has no bezel, so the wall only has to hold the picture. For a television in the same room — the TV size calculator.
Throw ratio, in plain terms
The throw ratio is the distance from the lens to the screen, divided by the width of the picture. A projector with a ratio of 1.5 needs 1.5 m between its lens and the wall for every metre of picture width, so three metres of throw makes a picture two metres wide.
A ratio below 1 is a short throw, which sits close to the screen. A ratio above 1.5 needs noticeably more room between the lens and the wall. The ratio is on the spec sheet, usually as a single number or as a range.
Measuring the throw
Measure from the front of the lens, in a straight line, to the surface the picture lands on. If the picture goes on a wall rather than a screen, measure to the wall.
Most projectors have a zoom, and the spec sheet then gives a range of ratios. Use the ratio for the zoom setting you will actually use: at the same distance, a different zoom gives a different picture width.
Reading the picture
Width comes from the distance and the ratio. Height comes from the aspect ratio, which is 16:9 unless you change it. A 16:9 picture 200 cm wide is 112.5 cm tall and about 90 inches across the diagonal, which is the figure screens are sold by. The same 200 cm width in 4:3 is 150 cm tall, and in 2.35:1 it is about 85 cm tall.
Pick the aspect ratio your content uses. A 2.35:1 film on a 16:9 picture is letterboxed, with black bars above and below it.
Where to sit for films
The sit figure is a range of distances, not one. It is the band the TV calculator uses for films at this picture width: near enough that the picture fills a useful part of your view, and far enough that it never fills more than is comfortable. The lower figure is the nearer seat and the upper one the further.
What the drawing does not check
The picture is drawn on the wall at true scale, with the lens position and the seating range marked. It does not allow for lens shift, which moves the picture up or down without moving the projector. A projector with lens shift can put the picture higher or lower than the drawing shows, so check the shift range on your model before you fix a mount.