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How to Calculate Projector Throw Distance

A crucial element in setting up your presentation

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Will you find out which projector lens is needed? Would you like to measure how large the projected image will get, or how far you need to position the projector?

  • 4:3, 16:9, it does not matter. Using the screen width assumes this is the largest dimension of the screen.
  • Throw distance is calculated from the projector lens to the screen.

Throw Ratio tells us what image size we can project from a certain distance away. For instance, a throw ratio of 1.5 indicates that for every 1 foot of image width, the throw distance must be 1.5 feet. The smaller the throw ratio, the larger the image a projector will produce at a shorter throw distance.


A projector’s distance from the lens to the screen surface is called the Throw Distance. The throw distance and the size of the image it produces on the screen are proportional to each other based on the optics of the lens. As you increase the distance between the projector lens and the screen the image will also increase.


A projector’s distance from a screen and the size of the image it produces are proportional to each other based on the optics of the lens. As you increase the distance between the projector and a screen the image will also increase.

If your projector has a zoom lens, the lens can be adjusted to change the size of the screen image without changing the distance of the projector. Since each projector lens is different, an online projection calculator tool will help you calculate the size of an image on a screen relative to how far the projector is placed from screen.


For any given projector, the width of the image (W) relative to the throw distance (D) is know as the throw ratio D/W or distance over width. So for example, the most common projector throw ratio is 2.0.

This means that for each foot of image width, the projector needs to be 2 feet away or D/W = 2/1 = 2.0. So if I’m using a projector with a throw ratio of 2.0 and I have an image width of 5 feet, then my throw distance must be 10 feet.

So the throw ratio is a simple formula that let’s you easily compute throw distance or image width given that you know one of these measurements.

A projector zoom lens will have two different throw ratios, one for the minimum zoom setting and one for the maximum zoom setting.


A short throw projector is a projector with a lens that has a throw ratio of 0.4 (distance/width) or less.

These projectors are ideal for rear screen applications where the area behind the screen is limited, or for a wall mounted application where the projector will be mounted within 1 or 2 feet from the screen.

The goal of these projectors is to produce as large of an image within the shortest amount of space between the projector and the screen.


Perhaps you bought your projector and installed it, intending to project directly onto your wall. While this may work for some people, you may decide you want to purchase a screen for your projected image to be displayed on.

Finding the optimal screen size is just as easy as discovering throw ratio and distance.

Distance / Throw Ratio = Width

After measuring the distance between the screen location and your projector, divide that by the throw ratio. This will provide you with the optimal width of the screen you should purchase.


A longer throw distance allows for smaller, sharper images to be projected from further distances away.

A longer throw lens is preferable if you intend to use your projector in large, expansive surroundings such as in large conference rooms or houses of worship where the projector is required to be hidden at the back of the building.

In these situations a long throw lens will most likely be required to make sure that the quality of the projected image is maintained while moving the projector further away from the screen.


A shorter throw distance will result in a bigger picture being projected, if the distance between the projector and the projection screen is kept constant. For further effect a short throw lens can be used to project an even larger image.

Some projectors come pre-installed with a short throw lens and can thus project a 48-inch diagonally wide image from only 4 feet way.

Projectors with short throw distances are suited to those people that require portability, such as road warriors, or for those people that need to use their projector and screen in smaller environments such as modest home theatre rooms, hotel rooms or small meeting rooms.

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