Part 1: No explanation needed, just give me the answer

When I first started designing audiovisual systems, I had a difficult time finding an article that helped me determine the correct display size for professional AV environments. So here it is in its simplest form:

That’s it. Once you have the minimal screen height as calculated by the above formula, you can then review the projection screen or TV specification sheet to determine what size display has the same height that you just computed.

For example, if the furthest seat away from the screen in your conference room is 18’. Simply divide 18’ by 6 which equals 3’. So, the height of your screen should be a minimum of 3’ or 36” tall. Then, simply Google 60” TV or 70” TV and read the dimensions of the display. You’ll find that a 70” display is 36” tall, so this room should have a minimum 70” display.

For end users and even the majority of AV integrators, this method will suffice. For true audiovisual designers, it’s blasphemous as not only has AVIXA established a new standard for calculating screen size, but even the original complete method is significantly more in-depth, includes numerous other calculations, and, of course, never includes Googling anything.

But hey, sometimes, you just want a quick answer and this will give it to you.

Part 2: Give me the details

Before we dive into the details, if you’re asking why I did not use AVIXA’s new formula for BDM (basic decision making) screen size it’s because the majority of people will not define the percentage of element height in relation to the image height and that’s a required variable in the new formula. The previous formula outlined in Part 1 will provide almost an identical answer to the newer model as long as you’re calculating for a display with HD 1920×1080 resolution, which at this time is the most common resolution.

However, what if you were presenting medical images, CAD drawings, engineering documents or other material that required detailed inspection rather than basic presentation material such as PowerPoint, websites, or Excel? We can use AVIXA’s new formula for ADM (Analytical Decision Making).

Using the same distance to furthest viewer (18’) from part 1 we would calculate,

Instead of Googling spec sheets from tv and projection screen manufacturers to find the right answer, you can solve for the screen size mathematically. Since we know we a need a minimum screen height of 68” and we know that HD displays have a 16:9 format, we can simply cross multiply to find the width.So, the minimum width of our screen is 120”. Now that we know the screen height (68”) and screen width (120”), we can use Pythagorean’s Theorem (a2+b2=c2) to calculate the diagonal.

So, we would require a minimum of a 138” screen as opposed to a 70” display for the same size room if we will be performing detailed investigation of content. That’s a big difference in display size, so it’s very important to determine what content you plan on displaying in the room prior to performing any calculations.

Now let’s investigate some additional considerations that will provide users a more ergonomic experience in basic decision-making mode.

While the distance to the furthest viewer is required to calculate screen size, the width of the display will determine the minimal distance the nearest viewer must be for comfortable viewing. If we go back to the example in Part 1, we have a 70” display that is 36” tall and 62” wide. A quick roll of thumb for calculating nearest viewer distance is to make sure the viewer is no closer than the width of the screen. In this case, the TV is 62” wide so the nearest viewer should be at least 62” or 5.2’ away from the display. Any closer than this, the nearest viewer will encounter eye fatigue along with not being able to see the entire screen within their natural field of vision.

The closest viewer should be no closer to the display than the width of the screen.

In addition to the nearest viewer needing to be a minimum distance away from the display, the nearest viewer should also be able to comfortably see the display by looking straight ahead. The human eye’s visual field on the vertical axis is most comfortable when viewing an image 30 degrees above to 40 degrees below the 0 degree line (straight ahead). Since the display is more than likely in a conference room, classroom, training room, or any other type of environment where there will be individuals seated or standing in front of you, the 40 degrees below the 0 degree line is eliminated since the individuals in front of you will prevent you from seeing the display. We’re left with field of 0 degrees to 30 degrees above for field of view for the room. So, in additional to determining the closest distance a person can sit to comfortably view the display, we must also ensure that the top of the display is no higher than the nearest viewer’s vertical viewing angle of 30 degrees. I would suggest doing this in CAD to make things easy.

Closest viewer should have an angle of 30 degrees or below from the top of the screen for ergonomic viewing

The information above is for standard sized rooms with standard dimensions. If you have a very wide room, a very long room, tiered seating, large windows, low ceilings, tall ceilings, high resolutions, unique resolutions, or any other less common attributes then additional considerations would be required.

All formulas referenced are from AVIXA, the formal trade association of the audiovisual industry.

Bill McIntosh, CTS-D
BrightTree Studios