Free tool
Projector throw & brightness calculator
Place the projector and size the screen in one step. Enter a throw ratio and either the image width or the distance you have, and get the screen size, the diagonal in metres and inches, and the ANSI lumens the room actually needs. Free, and nothing leaves your browser.
Throw distance
4.50 m
Image height
1.69 m
Diagonal
3.44 m (136")
Required brightness
1600 ANSI lm
Brightness assumes a matte, evenly lit screen. Manufacturer lumen figures are optimistic, so specify with headroom and check the projector's own throw ratio range before you fix the mount.
Two numbers decide the room: distance and light
Nearly every projector complaint traces back to one of two things. Either the mount sits at a distance the lens cannot fill, so the image is cropped or the front row is blinded, or the projector is simply too dim for the daylight in the room and the picture washes out by mid morning. Both are settled on paper, before anything is ordered.
The formulas
- Throw distance = throw ratio × image width, so image width = distance ÷ throw ratio.
- Image height = width ÷ aspect ratio, and the diagonal follows from Pythagoras.
- Lumens = target nits × screen area in m² × pi ÷ screen gain.
- Area scales with the square of the width, so a slightly bigger screen costs a lot more light.
Results are metric first with the diagonal in inches, because screens are sold in inches and rooms are measured in metres. For the background on the units, see lumens and throw ratio. Planning a whole room? Avitly puts the projector and the screen on the real floor plan, so the throw distance you calculate here is the one that gets installed.
Common questions
What is a throw ratio?
Throw ratio is the throw distance divided by the image width. A 1.5 ratio means the projector sits 1.5 metres back for every metre of image width, so a 3 metre wide image needs 4.5 metres of distance. Most standard lenses land between 1.2 and 2.0, short throw sits near 0.5, and ultra short throw goes below 0.4. Zoom lenses give a range instead of a single number, so check both ends against your mounting position.
How many lumens do I actually need?
It depends on screen area and how much light is already in the room, not on the diagonal alone. The calculator uses lumens = target luminance in nits, times screen area in square metres, times pi, divided by screen gain. A dark room is comfortable around 50 nits, a dim room around 100, a normal office around 150, and a bright room with daylight needs about 200. Doubling the image width quadruples the area, so it quadruples the lumens you need.
Does the calculator use the manufacturer's lumen figure?
No, and that is deliberate. Datasheet lumens are measured in a lab, at maximum lamp power, in the brightest and least accurate picture mode. In a calibrated preset with the lamp on eco you often see 60 to 70 percent of the printed number, and lamps lose output as they age. Treat the result here as the light you need on screen, then specify a projector with real headroom above it.
What does screen gain change?
Gain is how much light the screen reflects back toward the audience compared with a perfect matte white surface. A 1.0 matte screen spreads light evenly in every direction. A 1.3 or higher gain screen concentrates it toward the centre seats, so it reads brighter on axis but falls off for anyone sitting wide, and it can show hot spotting. High gain buys you brightness for free on paper, at the cost of viewing angle, so use it only when the seating is narrow.
How do I pick a screen size for the room?
Work back from the furthest seat and the smallest text on screen. A common planning rule for detailed content like spreadsheets and CAD is that the furthest viewer sits no more than four to six times the image height away. Then check the front row: closer than about 1.5 times the image height and people are turning their heads to read. Set the image height first, and the width and diagonal follow from the aspect ratio.
When should I stop specifying a projector?
When the calculator asks for more than roughly 10,000 lumens, or when the room cannot be darkened at all. At that point a laser projector is the honest minimum, and a direct-view LED wall is often the better answer: no lamp replacement, no throw distance to protect, no shadow when someone walks past, and consistent output for years. The install cost is higher, the ten year cost frequently is not.
Design it once. Sell it, install it, service it.
Avitly runs the whole install off one floor plan: quote, client-signed offer, bill of materials, rack layout, then device credentials and tickets after handover. Presales to maintenance, no re-entry.
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