Projector Throw Distance Calculator
Work out how far to place a projector for a screen size, or the image size at a distance, from the throw ratio or zoom range, plus brightness in foot-lamberts.
Measure from the front of the lens to the screen; some makers measure from the back of the case — check the manual.
Bright enough for a room with some ambient light.
Spec-sheet lumens are measured in the brightest mode; calibrated modes are often 20–40% dimmer.
A projector's throw ratio fixes how big the picture is at a given distance. This calculator tells you where to mount the projector for the screen you want — as a range if the lens zooms — or how big the image will be from where it can go. Add the lumen rating and screen gain to check whether the picture will be bright enough, in foot-lamberts and nits.
How to use this tool
- Enter the throw ratio from the spec sheet; for a zoom lens enter both ends.
- Choose "Distance for a screen size" and enter the diagonal or width, or choose "Image size at a distance" and enter the distance.
- Pick the aspect ratio of the picture.
- Optionally enter lumens and screen gain to check brightness.
Formula
distance = throw ratio × image width · width = diagonal × a ÷ √(a² + b²) · brightness (fL) = lumens × gain ÷ area (sq ft) · nits = fL × 3.426
a:b is the aspect ratio (16:9 → width = diagonal × 0.8716). A throw ratio below 1 is short-throw; below about 0.4 is ultra-short-throw. One foot-lambert is 3.426 candela per square metre (nits).
Example
A projector with a 1.5 throw ratio filling a 100-inch 16:9 screen (87.16 in wide) must sit 1.5 × 87.16 = 130.7 in (3.32 m, 10.9 ft) away. With 2,000 lumens on a 1.0-gain screen of 29.7 sq ft, the image measures about 67.4 fL (231 nits) — plenty for a dim living room. A 1.32–2.15 zoom lens can be placed anywhere from 2.92 to 4.76 m.
Frequently asked questions
Where do I find the throw ratio?
In the specifications or manual, usually written like "1.50:1" or "1.32–2.15". Some makers also publish their own distance calculator for exact lens offsets.
How bright should the picture be?
About 16 fL is the cinema reference for a dark room; with some daylight or lamps on, 30–50 fL looks much better. Higher-gain or ambient-light-rejecting screens help.
Does keystone correction change this?
Digital keystone shrinks the image and softens it. Position the projector so the lens is centred, or use lens shift if it has one.
Last updated:
Page address with these inputs: https://kakao.mobile/tools/projector-calculator/
Cite or embed this tool
kakaoCalc. (2026, November 8). Projector Throw Distance Calculator. https://kakao.mobile/tools/projector-calculator/
“Projector Throw Distance Calculator.” kakaoCalc, 8 Nov. 2026, kakao.mobile/tools/projector-calculator/.
Paste this code into your page. The widget runs in your visitors' browsers, shows no ads and keeps a link back to this page. Embedding terms