How to calculate projector throw

Written by patrick hutchison
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How to calculate projector throw
Get your screen size just right by calculating your projector's throw. (FrareDavis Photography/Brand X Pictures/Getty Images)

Home theatre projectors mimic the larger-than-life experience of being in a real theatre. You can create huge images in relatively small spaces with most home theatre projectors. In order to determine the screen size you can create with your home theatre project, calculate its throw. A projectors throw, or throw ratio, is a measurement of how large the projector image will be, given a certain distance from the screen. Projector throws are often referred to as throw ratios because most projectors can zoom in and out to create minor adjustments in the size of images without changing distance to the screen.

Skill level:
Moderately Easy

Things you need

  • Measuring tape
  • Calculator

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  1. 1

    Turn your projector on, and project an image onto your screen or a blank wall.

  2. 2

    Measure the distance between your projector and the screen with a measuring tape. Record the distance in inches.

  3. 3

    Adjust your projector's zoom to make the image as small as possible, and measure the width of the projected image in inches.

  4. 4

    Adjust your projector's zoom to make the image as large as possible, and measure the width of the projected image in inches.

  5. 5

    Calculate your projector's throw ratio with a calculator by dividing the distance from projector to screen by the width of the projected image. Calculate two ratios, one for minimum zoom and one for maximum zoom using the following equations and examples.

    Distance from projector to screen in inches / Image width in inches = Projector throw ratio

    For example, a projector that is 120 inches away from a screen, creating image sizes from 60 inches wide to 80 inches wide, would have a projector throw ratio of 1.5:1-2:1. (120 / 80) to (120 / 60):1

Tips and warnings

  • Use your throw ratio to find how far away your projector should be to create your desired screen size. For example, if your projector has a throw ratio of 1.5-2:1 and you want an image that is 90 inches across, you will need to put the projector anywhere between 135 and 180 inches from your screen.
  • Screen width x Throw ratio = Distance to screen.
  • Do not move your projector after it has warmed up. The expensive bulbs inside are more fragile after they have heated up. Moving a warm projector may increase the chance of breaking a bulb.

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