Calculating Throw Ratio from Focal Length

The throw ratio of a projector can be calculated from the focal length of the lens and the diagonal size of the LCD/LCoS/DLP panel.

Note that a zoom lens has two focal lengths, one corresponding to the wide-angle position and one to the tele-position.

For a 16:9 screen, the throw ratio is approximately: 1.15 * focal length / panel diagonal
For a 4:3 screen the throw ratio is approximately: 1.25 * focal length / panel diagonal

The focal length and panel diagonal must be expressed in the same unit (e.g. mm)

Note that this formula is an approximation. Always check the actual throw ratio with the manufacturer.

Example Using a 16:9 screen, and a projector with a lens with focal length 28mm - 38mm, and a 0.9" LCD panel, what is the throw ratio range? 0.9" = 22.9mm Smallest throw ratio = 28 / 22.9 * 1.15 = 1.41 Largest throw ratio = 38 / 22.9 * 1.15 = 1.91 The throw ratio range is approximately: 1.41 - 1.91

Other Projector Facts

Lens Shift
Keystone Correction
Throw Ratio and Zoom Range
Min and Max Throw Distance
Calculating Screen Brightness
Sufficient Brightness

[All notes on one page for easier printing]