Video and displays
Throw ratio
The distance from the projector lens to the screen divided by the image width, which tells you how far back a projector must sit.
Throw ratio equals throw distance divided by image width. A 1.5:1 projector needs 1.5 m of distance for every 1 m of picture width. Zoom lenses cover a range, for example 1.3 to 2.1, so the projector can sit anywhere in a band of positions.
The ratio decides whether a projector can live on a rear shelf, on the ceiling, or on a table below the screen. Get it wrong and the image is the wrong size with no fix short of moving the mount.
Standard-throw home projectors fall between about 1.2 and 2.2, short-throw around 0.5 to 1.0, and ultra short throw below 0.4. For a 100 inch 16:9 screen (87 inch wide), a 1.5 ratio puts the lens about 131 inches, or 3.3 m, away.
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