Projector Throw Distance Calculator
Where does the projector go? Screen width × throw ratio gives the distance.
How projector throw distance works
A projector lens has a throw ratio — the distance to the screen divided by the screen width. A lens with a fixed ratio must sit at exactly that distance; a zoom lens gives a range (the min and max ratio), so you can place the projector anywhere inside that spread. The distance is simplythrow distance = screen width × throw ratio, and the reverse is screen width = throw distance ÷ throw ratio.
Because the screen is usually described by its diagonal, the calculator first turns the diagonal into a width using the aspect ratio:width = diagonal × W ÷ √(W² + H²). A 120″ 16:9 screen is about 104.6″ (2.66 m) wide. A standard-throw projector has a ratio above 0.4; an ultra short throw (UST) projector is 0.4 or below and sits just inches from the wall.
The preset list gives common Epson, BenQ, Optoma, Panasonic and Sony models so you can start from a real lens instead of guessing a ratio — the figures are planning values from the manufacturer spec sheets, so always confirm the exact number for your specific unit.
Worked example
A 120″ 16:9 screen is 2.66 m wide. With a zoom lens of 1.13–1.47, the projector can sit anywhere from 2.66 × 1.13 = 3.00 m to 2.66 × 1.47 = 3.91 m from the screen. The same screen on an ultra-short-throw lens (ratio 0.4) needs only 2.66 × 0.4 =1.06 m. Working backwards, a 3.50 m throw with a 1.30 ratio supports a screen width of 3.50 ÷ 1.30 = 2.69 m (about 106″).
Frequently asked questions
What is throw ratio?
Throw ratio is the projector lens’s throw distance divided by the screen width — a 1.5 ratio means the projector sits 1.5× the screen width away. A range (e.g. 1.13–1.47) means the lens has zoom, so you have placement flexibility.
How do I turn a diagonal size into a screen width?
Use the aspect ratio: width = diagonal × W ÷ √(W² + H²). A 120″ 16:9 screen is 120 × 16 ÷ √(16² + 9²) ≈ 104.6″ ≈ 2.66 m wide. This calculator does that step automatically when you enter a diagonal.
What is an ultra short throw (UST) projector?
A projector with a throw ratio of 0.4 or less. It sits inches from the wall and throws a large image from almost no distance — ideal for living rooms where no one can walk through the beam.
Do I need a zoom lens?
A zoom lens gives a throw-ratio range, so one projector works across a spread of room sizes. A fixed-ratio projector has a single ratio and must be placed at exactly that distance for a given width.
How accurate are the preset ratios?
They are planning values from manufacturer spec sheets. Different lens shift, zoom and mount offsets can change the practical distance, so confirm the exact figure on the current datasheet before ordering.
Related calculators
- Display Setup Simulator — the full plan: viewing distance, brightness and room layout.
- Screen Size Calculator — convert a diagonal, width and height for any aspect ratio.
Disclaimer: throw ratios and distances are planning estimates. Confirm the exact ratio, lens shift and mount offset with your projector manufacturer before ordering.