Tilt and Keystone Distortion Calculator for Projectors

This Javascript calculator determines the amount of tilt or pitch needed to raise a projected image a given height. It also determines the resulting keystone image distortion. These can be important considerations, particularly for rooms with low ceilings and high offset projectors.

How To Use this Calculator

In the input section, enter the lens drop, image drop, image height, and throw distance as shown in the diagram, assuming no tilt. These numbers can be determined from projector calculators such as this web-based one at projector central or this Mitsubishi-specific one (requires installation). Also, enter the amount by which you wish to raise the image. It actually doesn't matter which units you use as long as you're consistent.
Hit "calculate" to see the amount of tilt from horizontal necessary to raise the image, and the resulting image distortion. Note that the resulting image will be smaller than nominal in all three dimensions (top width, bottom width, and height). Most likely you can compensate for one or more of these by using a small amount of zoom. The dimensions of the resulting zoomed images are shown at the bottom. Most people find image spill over onto the border to be less distracting than having parts of the screen unlit.

Important Notes

Use this guide at your own risk. Double check all measurements and calculations yourself before spending any money on a projector or screen. Also, set up the projector and screen in a temporary fashion to check image size and placement BEFORE you start hammering, drilling, and sawing.
The calculator assumes that the zoom scales the image while keeping the offset constant. This is generally true, but there may be projectors that work differently.
The calculator asks for the desired distance to raise top of image, but if you instead want to lower the image, simply input a negative number.
Comments, corrections, and suggestions are welcome and should be sent to "smspam @ comcast . net" with "projector calculator" in the subject line.

Less Important Notes

The calculator gives the needed tilt angle in degrees. This is FYI only, you will not need to measure this angle, and would be pressed to do so accurately anyway. Rather, just simply mark the spot on the wall/screen where you want the image top to be, turn the projector on, and tilt it until it lines up.
All else being equal, the greater the throw, the less keystone distortion for a rise in image height. So if some tilt will be necessary, it's best to mount your projector towards the long end of the throw range, given the available zoom. Leave yourself some wiggle room just in case, though, and as mentioned above, test the setup before making things permanent.
Note that keystoning can also be compensated for by tilting the screen slightly.

Inputs

(1) Drop from ceiling to lens center:

(2) Distance from ceiling to top of image:

(3) Image height: Width:
Screen size quickset:

(4) Throw distance (lens to screen):

Desired distance to raise top of image:

Units: