How is projector throw distance calculated?

Throw distance = throw ratio × image width. A projector with a 1.3:1 throw ratio filling a 100-inch 16:9 screen (87 inches wide) mounts about 113 inches — 9.4 feet — from the screen. Zoom lenses give a min–max ratio range.

How far should viewers sit from the screen?

A common guideline is 1.5–1.9 times the screen width for comfortable viewing of HD/4K content — closer for cinema immersion (THX ~1.5×), farther for text-heavy boardroom content (up to ~2.4×).

Projector Throw Distance & Screen Size Calculator

Q: What is a short throw projector?

Short throw projectors have ratios around 0.4–0.8, producing a big image from a metre or so away; ultra-short-throw units (below 0.4) sit on a credenza directly beneath the screen. They suit small boardrooms where a ceiling mount would put the projector in the presenter's sight line.

Enter the projector's throw ratio and your screen size to get the mounting distance range, exact screen dimensions and the seating distances that make the image comfortable to watch.

Projector & screen

Throw ratio — min (wide)

From the projector spec sheet, e.g. “1.2–1.5:1”.

Throw ratio — max (tele)

Screen diagonal

Units

Aspect ratio

Ratios: <0.4 = ultra short throw · 0.4–0.8 = short throw · 1.2–1.6 = standard boardroom zoom · >2 = long throw.

Placement & screen

—

projector lens to screen

Screen width—

Screen height—

Closest comfortable seat (~1.5× width)—

Farthest comfortable seat (~1.9× width)—

Throw category—

Distances are lens-to-screen. Allow extra for the projector body and rear connections when planning the mount point.

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Getting projector placement right the first time

Throw distance mistakes are the most common reason AV installs need a second visit: the mount goes in, the image lands 15% too small, and now there's a ceiling anchor in the wrong place. Always compute the throw range from the specific projector model's ratio — “about mid-room” is not a spec — and confirm the zoom range covers your screen with margin at both ends.

Rules of thumb

Screen size from seating: farthest viewer ÷ 1.9 ≈ minimum screen width. A boardroom with viewers 16 ft away wants a screen at least ~100" wide (115" diagonal in 16:9).
Text legibility: for spreadsheets and dashboards, keep the farthest seat within ~2.4× screen width, closer than the movie-watching limit.
Lens shift beats keystone: physical lens shift preserves resolution; digital keystone correction throws pixels away. Mount square to the screen whenever possible.
Ambient light: a bright boardroom needs roughly double the lumens of a dim theatre for the same perceived image; ALR screens help flat-panel-like daytime performance.

Frequently asked questions

How is throw distance calculated?

Throw = ratio × image width. A 1.3:1 ratio on an 87"-wide screen means ~113" (9.4 ft) lens-to-screen.

What is a short throw projector?

Ratio ~0.4–0.8 — big image from about a metre away. Ultra short throw (<0.4) sits directly below the screen.

How far should viewers sit?

Roughly 1.5–1.9× the screen width for video; up to ~2.4× is fine for presentations with large text.

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