Projector throw distance

How it is worked out

Throw distance = throw ratio × picture width. A throw ratio of 1.5:1 means the lens sits 1.5 m away for every metre of picture width. A zoom lens has a range (for example 1.4–2.1:1), so the projector can sit anywhere in a band of distances for the same picture; the short end gives the biggest picture from a given spot.

The distance is from the front of the lens to the screen. Leave room behind the projector for cables and ventilation; the room check keeps 0.3 m, a rule of thumb.

Things the ratio does not tell you

• Lens offset and shift: how high or low the projector must be relative to the screen. Check the manual before fixing a ceiling mount.
• Scope screens: with the zoom method a 16:9 projector is zoomed until 2.39:1 films fill the width, so use the scope screen's width (choose 2.39:1 above).
• Brightness: a bigger picture is dimmer. The same projector looks brighter on a smaller screen or a higher-gain screen.