There are several factors in sizing your projection screen: The size and layout of the room; the media to be projected; audience location in relation to the screen; and projection format must all be considered. These factors can for the most part be boiled down to two main things to consider: dimensions of the audience area, and the projection format to be used. In some cases, these two questions will lead to the same conclusion; in others they will not, and compromises will have to be made.

Height

The first thing to figure out is the screen height, that is, the size of the viewing surface from top to bottom. If you plan to be showing standard video (4:3) entertainment, screen height should be at least 1/6 the distance from the screen to the furthest seat; for HDTV projection (16:9), screen height should equal or exceed 1/3 the distance from the screen to the optimum seat–the best seat in the house!

Width

Screen width is generally determined by the height of the screen, and the projection format to be used. To figure out what the screen width will be, use the formulas found in the “Screen Size Formulas” chart.

Ceiling Height

The bottom of the screen should be approximately 40-48" above the floor in a room with a level floor and several rows of seats. In home theatres with sloped floors, or small rooms with only one or two rows, the bottom of the screen should usually be 24-36" above the floor. Evaluate any barriers, and try to make sure that the lower part of the screen will be visible from all seats. If the room has a particularly high ceiling, “extra drop,” or extra material at the top of the screen, may be required to position the screen at a comfortable viewing level.

Projection Format

Once you know roughly how big the screen needs to be based on the audience area, that size may be modified based on the projection equipment you’ll be using. If the screen will only be used with one type of projector (NTSC video, for example), determining exact screen dimensions is relatively simple. Projection formats are expressed in terms of aspect ratio, which is the relationship of the height of the projected image to its width. Aspect ratios of common projection formats, and formulas for determining various screen dimensions, can be found in the “Screen Size Formulas” chart.

For Example

Let’s say you have a home theatre, and want an HDTV (16:9) screen. For argument’s sake, we’ll put the best seat 12 feet from the screen. That means the screen height should be 1/3 of the distance from the best seat to screen. You already determined that’s 12 feet; now you know the screen height will be roughly 4’, or 48”. Given that the HDTV 16:9 ratio, the screen width will be about 85”, with a diagonal measurement of 98”.

Terry Coffey handles Media Relations and Technical Publications for Draper, Inc., a manufacturer of projection screens, lifts and mounts for projectors and flat panel displays, window shades and gymnasium equipment.

Chart:

Screen Size Formulas

Listed below are projection formats and their respective ratios (height vs. width).

Once you know the screen height, use the following formulas to figure out the other screen dimensions (D = exact diagonal; H = viewing area height; W = viewing area width).