Projector Throw Lab

Throw distance is the distance between the projector's lens and the screen surface. It is measured from the front of the lens — not from the front or back of the projector body — to the screen. Throw distance, together with the projector's throw ratio, determines how large the projected image will be.

Throw ratio is throw distance divided by image width, using the same units for both: TR = throw distance / image width. For example, a projector 12 feet from the screen producing a 7-foot-wide image has a throw ratio of 12 / 7 = 1.71:1. Rearranged, throw distance = TR x image width, and image width = throw distance / TR.

It depends on your room, not on quality. Typical bands: ultra-short throw 0.2-0.45:1 (inches from the wall), short throw 0.6-1.2:1 (a few feet from the screen), and standard/long throw 1.2-2.5:1 (the most common home-theater class, often with zoom). Pick the band that fits where you can physically place the projector.

A common planning rule: screen width about 1/2 to 2/3 of your viewing (seating) distance. More formally, SMPTE recommends a 30-degree horizontal viewing angle and THX recommends 36 degrees. For 16:9, that works out to roughly 0.62x viewing distance for SMPTE and 0.75x for THX as screen diagonal. Use the Room Planner tab: enter your seating distance and it suggests a diagonal range for both standards. Example: a bedroom with an 8-foot viewing distance points to roughly a 59-72 inch diagonal by these standards.

Measure the farthest distance you can place the projector lens from the wall (your throw distance), then divide by the throw-ratio band of the projector class you are considering: image width = throw distance / throw ratio. A smaller ratio gives a bigger image from the same spot. The Room Reverse Solver tab does this for all three projector classes at once and converts width to diagonal for 16:9, 16:10, or 2.35:1.

A short throw projector has a throw ratio roughly between 0.6:1 and 1.2:1, so it can sit just a few feet from the screen. Example: at 0.8:1, a 90-inch 16:9 screen (about 78.6 inches wide) needs only about 5.2 feet of throw distance. Short throw is the fix for small rooms where a standard projector would have to sit behind the couch.

A UST projector has a throw ratio around 0.2-0.45:1 and sits inches — not feet — from the wall, usually in a low console directly below the screen, projecting upward. Example: at 0.25:1, a 120-inch 16:9 screen needs only about 26 inches of throw distance. UST setups pair best with ambient-light-rejecting (ALR) screens, because the steep projection angle is what ALR screens are designed for.

A zoom lens gives a range of throw ratios instead of one fixed number. If a projector is rated 1.2:1 with 1.3x zoom, its throw ratio spans 1.2:1 (widest) to 1.56:1 (most zoomed in). For a fixed screen size, that means a range of valid mounting distances: minimum distance = base ratio x image width, maximum = base ratio x zoom x image width. The Zoom Range tab visualizes this as a bar.

Yes. Find the throw ratio (or throw-ratio range) on your model's spec sheet — it is usually listed as something like '1.15-1.5:1' — and enter it here. This lab is model-agnostic: it does the planning math for any ratio. If you want a calculator that already knows your exact model's specs from a database, ProjectorCentral's per-model throw calculator is the right tool for that job.

Measure from the projector's lens to the screen surface in a straight line, using the same units as your image width (feet, meters, or inches). Ignore the projector's body depth — only the lens position matters. For ceiling mounts, the horizontal distance is what counts; keystone or lens shift do not change the throw-distance math.

There is no single number — maximum throw distance = maximum throw ratio x image width. A projector rated 1.2-2.5:1 throwing a 7-foot-wide image can sit between 8.4 and 17.5 feet away. Zoom out to the widest setting for the shortest distance; zoom in (telephoto) for the farthest. Mounting beyond the maximum gives an image larger than your screen.

16:9 matches HDTV, 4K UHD, streaming, and games — the right default for most home theaters. 16:10 fits PC presentations. 2.35:1 (CinemaScope) matches widescreen films with no letterbox bars but needs an anamorphic setup or zooming for 16:9 content. For the same diagonal, 2.35:1 gives a wider but shorter image than 16:9; the Screen Size tab converts diagonal to exact width and height for each.

It depends on room light more than screen size, but the math is a useful sanity check: divide lumens by screen area in square meters to get lux on the screen. As a rough guide, around 50+ lux works in a dark room, 100+ lux tolerates some ambient light. For example, 2,000 lumens on a 100-inch 16:9 screen gives about 725 lux (roughly 230 nits at gain 1.0) — plenty for a dark room. The Brightness tab computes this for your exact setup.

Yes, indirectly. The projector outputs the same lumens, but a longer throw (or lower throw ratio setting via zoom) spreads those lumens over a larger image area, so brightness per square meter drops. Doubling the image width quadruples the area and quarters the brightness. That is why the brightness sanity check uses your actual screen size, not just the lumen rating.

Too close (below the zoom range minimum) means the image cannot shrink enough to fit your screen — you would need a smaller screen or a projector with a lower throw ratio. Too far (beyond the maximum) means the image overflows the screen even at full telephoto zoom. The safe mounting zone is exactly the zoom-range bar the calculator shows.

ProjectorCentral's calculator is per-model: you pick your projector from their database and it computes distances from that model's exact specs — unbeatable if you already own the projector. This lab is model-agnostic and planning-oriented: ratio math for any projector, UST mode, a reverse solver (room distance to screen size), a zoom-range visualizer, and screen/brightness tools in one place. Use this lab while planning; use theirs to double-check a specific model.