Enter either how far the projector will sit from the wall, or the screen size you want, and this works out the other side of the equation — plus how far back you should actually sit.
Based on the standard throw-ratio formula (distance ÷ image width) manufacturers use to publish their own specs. Actual placement varies slightly by model due to lens offset — confirm exact placement against the specific projector's manual before mounting a screen or drilling holes.
| Projector | Image size at this distance |
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Throw ratio is simply throw distance ÷ image width. A projector rated at 0.2:1 needs 0.2 feet of distance for every foot of image width — which is why ultra short throw projectors like the ones on our projector picks page can sit on a low console just inches from the wall and still throw a 100"+ image. A projector rated at 1.5:1, by contrast, needs to sit roughly a foot and a half back for every foot of image width, which is why standard-throw projectors are usually ceiling-mounted well back into the room.
Every projector's spec sheet lists this number, sometimes as a single fixed ratio (like the 0.2:1 shared by the Hisense PX4 Pro and both AWOL Aetherion models above) and sometimes as a range if the projector has an adjustable zoom lens (like the Epson Lifestudio Grand's 0.16–0.22:1). A zoom lens gives you a little flexibility in exact placement for a given screen size; a fixed ratio means the distance for a given size is locked.
16:9 is the right default for almost everyone — it matches streaming, broadcast TV, and most Blu-rays without black bars. 2.35:1 (Cinemascope) matches many theatrical films exactly and looks striking for movie-only viewing, but adds black bars above and below anything not shot in that ratio, which is most TV and a fair amount of film content too. Unless you're building a dedicated, movie-only room and specifically want a scope screen, stick with 16:9.
A screen that's the right size for a 12-foot room can feel oversized in an 8-foot one, and vice versa — the size number alone doesn't tell you whether it'll feel right. Two commonly cited standards frame the range: SMPTE recommends a 30-degree horizontal viewing angle, a slightly more relaxed setup better suited to mixed TV and sports viewing, while THX recommends up to 40 degrees for a more cinema-like, immersive feel that intentionally fills more of your peripheral vision.
In practice, that works out to sitting somewhere between roughly 1.4 times the screen's width (THX, closer and more immersive) and 1.9 times the screen's width (SMPTE, more relaxed) away from it. The calculator above gives you that full range for whatever screen size you land on — use the closer end if movies are the priority, the farther end if you'll also be watching a lot of sports or general TV on it.
Bigger isn't automatically better. Sitting closer than the THX range trades immersion for visible pixel structure and a picture that's uncomfortable to take in as a whole. If the math above puts your ideal seating distance outside where your couch actually is, it's worth adjusting the screen size to fit the room you have — not the other way around.