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How to calculate the distance from the projector to the screen

by Gaurav Gupta

The key to a pleasant pastime when watching your favorite video content lies in the correct relative placement of the projector and screen in the room. Before installing the projector in the selected room, it is necessary to determine the optimal point where the projector will be installed, and evaluate its spatial position relative to the screen. In doing so, a number of different criteria and parameters should be taken into account. These include:

  • screen size and room configuration,
  • some projector specifications such as throw distance and offset.

These parameters – their physical meaning and influence on the installation process – we will describe in this article.

First of all, before choosing where to place the projector and screen, we must answer one question for ourselves: what size image is most preferable for us. Next, you need to make sure that they are within the range that the throw ratio of the projector provides. This is one of the basic parameters of the device. Let’s talk about it a little more.

Throw ratio (PS)

The parameter is a fraction, the numerator of which is the width of the image (picture), and the denominator is the distance between the projector and the screen. Naturally, the range of acceptable PS values ​​is determined by the optical system of a particular projector equipped with an optical zoom. PS with the indication of the minimum and maximum values ​​​​are prescribed in the technical documentation for the projector. They are used to determine the distance between the lens and the projection screen and confirm the suitability of a particular projector in relation to the size of the existing room.

The working formula is as follows:

Throw Distance = Throw Ratio * Screen Width

If the characteristics of your device and the dimensions of the room fit into the above formula, then you will be able to form an image on the screen with the highest possible quality.

This formula can be put in a more practical form:

Screen width = throw distance / throw ratio

In this case, the screen and projector locations are selected first. And only then will you select a specific screen model with dimensions that lie within the allowable range of values. For example, you plan to place the entire set on two opposite walls of the room, the distance between which is 5 meters. In addition, you have a manual projector screen  with a throw ratio of 1.4/1…2.8/1. Substitute the values ​​in the formula and get:

  • 5 m / 1.4 ≈ 3.6 m,
  • 5 m / 2.8 ≈ 1.8 m.

It turns out that in this case we should look for a screen model with a width in the range from 1.8 to 3.6 m.

When choosing the location of the screen and the projector, it should be remembered that the farther apart they will be located, the larger the screen can be used.

Lens shift

It is the presence of this parameter in the list of device characteristics that determines the multi variance of the relative position of the projector and screen. And in the absence of it, the projector and screen will have to be positioned so that the optical axis of the lens coincides with the straight line restored from the center of the screen. Such a requirement severely limits the possibilities of relative positioning of home theater elements and does not contribute to comfortable viewing of video broadcasts. In addition, indoors, whether it is a room to an apartment, an office or a classroom, as a rule, there is furniture, sofas, seating areas for spectators, which further reduces the list of places for projector and screen installation .

These restrictions are lifted if the projector has such functions as:

  • keystone correction
  • lens shift.

The presence of a lens shift in the projector allows you to tilt the device vertically and / or horizontally relative to the screen plane, without degrading the image quality in any way.

In real terms, this means that by hanging the screen on the wall, you can place the projector almost anywhere:

  • hang from the ceiling or place on the wall,
  • put on a bedside table in any direction from the audience and the screen.

To calculate the allowable deviation distance from the central perpendicular axis of the screen, there are simple formulas:

Projector Installation Height = (Screen Height) * (Vertical Offset Percentage)

The specific value of the last term of the formula – the percentage of the vertical ratio, is reflected in the technical documentation. The signs “+” or “-” indicate the variant of the relative position of the projector and the screen: “+” – the projector is below the screen or the image is projected upwards, “-” the projector is above the screen.

The shift in the horizontal plane is calculated approximately by the following formula:

Projector Horizontal Offset = (Screen Width) * (Percent Horizontal Offset )

The possibility of horizontal shift is implemented in more expensive models with high functionality.

Nuances in determining the installation location of the projector

One of the most important steps in a home theater setup is determining where to install the projector:

  • Ceiling location of the projector significantly saves the space of the room, but requires reliable mounting to the ceiling and laying a cable line to the installation site. The fastening itself is carried out using a special mounting kit. For safety reasons, it is not recommended to place viewing areas under the installation site of the projector to avoid injury if the unit may fall. Such fastening is most widely used in business premises and offices.

For example, in the above photo, the projector is located away from the audience seats.

  • Short throw projectors are characterized by a small throw ratio. It does not exceed one, which allows you to install the projector in close proximity to the screen. The distance between them is a few centimeters. Such devices are best suited for home theaters and small meeting rooms.
  • Long throw projectorsare the exact opposite of short throw models. The projector’s long throw optics deliver crisp, high-quality images from long distances.

Screen selection

Screen selection features are a topic for a separate article. Here we note only a number of the most significant points that must be taken into account:

  • Keep the screen out of direct sunlight, or otherwise place heavy curtains over the windows.
  • The recommended height of the screen along its bottom edge is 60…90 cm.

The principles by which the optimal distance between the projector and the screen is calculated apply to all types of projection equipment, from premium models for home theaters to budget models for offices and classrooms.

After the preliminary calculation, you will only have to choose the right equipment, read about this  guide for choosing a projector . After reading, you will be able to choose and buy the right projector with a crane in any store.


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