Throw Ratio and Calculate the Projector’s Distance

Throw ratio is the distance (D) from the screen that a projector needs to be in order to create a specified size image. Or a projector’s throw ratio is defined as the distance (D), measured from lens to screen, that a projector is placed from the screen, divided by the width (W) of the image that it will project (D/W).

Each projector manufacturer has a choice of which type of lens to place on their projectors and, understandably, each lens has a different set of characteristics. One of the more important characteristics of a lens is its throw ratio. With throw ratio you can calculate the distance from projector to screen and size of screen that used.

The ratio, like any ratio, is dimensionless. For example, if D equals 10 feet and W equals 5 feet, then 10 feet divided by 5 feet equals 2. The dimension of “feet” is thereby cancelled out. So, in knowing this formula, a projector’s throw ratio will provide you with all of the information you’ll need to set up a room. The following examples will better explain how this works.

Example 1: You know what screen size you want, but need to know how far back the projector will need to be placed. If the screen width is 7 feet and the projector’s throw ratio is 2.0 – 2.4:1 (because projectors have zoom lenses, they also have a range of throw ratios) then you can place your projector anywhere from 14 to 16.8 feet away from the screen. (7 * 2 and 7 * 2.4 = 14-16.8)

Example 2: Maybe you don’t know which screen size want, but you do know that the space available in your room for projector placement is limited. The projector should be placed 15 feet away from the screen. So, how big of a screen can you use? If your projector has a throw ratio of 1.8 – 2.22:1, your screen can be between 6.76 and 8.33 feet wide. (15 / 2.22 and 15 / 1.8 = 6.76 and 8.33)

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