# How to Calculate the Throw Distance on a Projector

By Michael Carroll

i videoprojecteur image by mattmatt73 from Fotolia.com

Planning a home movie theater involves trade-offs and compromises determined by the space you have available, the technology's capabilities and your budget. The throw distance of a projector is the distance between the projector and the screen, and it's limited by the size of your room because the projector can't be further from the screen than the room's length. The throw distance also affects the size of the picture the projector makes on the screen, so it's prudent to make a few simple measurements and calculations in advance to get the best results with the space you have, and to help you decide on a projector to use.

Consult your projector's documentation and find its throw ratio. The throw ratio is the distance from the projector to the screen divided by the width of the image it produces on the screen at that distance. It is usually expressed as a decimal number, and as a range of numbers if the projector has a zoom lens.

Determine the width of the image you would like to project. You can use any measurement units you like.

Multiply the width of the image by the throw ratio to find the throw distance, expressed in the same units. If a range of throw ratios is specified, perform the multiplication separately on both numbers to find the range of possible distances at which the projector can produce an image of the correct size. You can then place the projector at a convenient distance from the screen within this range, adjusting the loom lens as necessary to get the image you planned for.