How Big Should Your Display Be? A Friendly Guide to the AVIXA DISCAS Standard

Written and technically reviewed by the avtecture AV engineering team. Last updated September 2026, based on ANSI/AVIXA V202.01:2016, the current published version of the DISCAS standard.

"What size screen do I need?" is the question we hear most often from clients planning a boardroom, classroom, or control room. It sounds like a matter of taste — pick whatever looks impressive, or whatever fits the budget. It isn't. It's a matter of math, and the math has been worked out for you.

As AV consultants, we size every display using DISCAS, the official AVIXA standard for calculating display image size. Below, we walk through exactly how it works — starting simple, then going as deep as you'd like to follow us.

Why "just buy the biggest TV you can afford" doesn't work

For years, the industry leaned on a rule of thumb called 4/6/8: take the distance to the farthest viewer and divide it by 4, 6, or 8 — depending on how detailed the content was — to get the minimum image height. It was quick, easy to remember, and completely undocumented. Nobody could really explain where the numbers 4, 6, and 8 came from, and the rule ignored something that has become far more important since it was invented: resolution. A 4K display and a 10-year-old projector were treated identically, as long as the room size was the same.

In 2016, AVIXA replaced this guesswork with a proper standard: ANSI/AVIXA V202.01:2016, Display Image Size for 2D Content in Audiovisual Systems — known by its short name, DISCAS. Instead of a rule of thumb, it's grounded in research on human visual acuity: how small a detail the human eye can actually resolve at a given distance. It's the method professional AV designers use when they need to defend a screen size on a drawing, not just recommend one.

The three questions DISCAS asks

Before any formula comes into play, DISCAS asks three plain-language questions:

1. Who is the farthest viewer, and how far away are they?

Simply the distance from the display to the back-most seat that still needs to see the content properly. Not the size of the room — the distance to the person who has to work hardest to see it.

2. What kind of decisions will people make from the content?

DISCAS defines two viewing categories:

• Basic Decision Making (BDM) — general content: slide decks, video calls, dashboards, word processing. Viewers need to grasp the overall picture, not read every character. In our experience, this covers roughly 80% of the rooms we design — most meeting rooms, classrooms, and huddle spaces fall here.
• Analytical Decision Making (ADM) — detail-critical content: CAD drawings, medical imaging, spreadsheets packed with small numbers, security or control-room feeds. Every pixel matters, because a missed detail has real consequences.

Think of it this way: BDM is "can everyone follow along?" ADM is "can everyone individually verify the smallest detail?"

3. How small is the smallest thing people need to read?

For BDM, this is expressed as %EH (Percent Element Height) — the height of the smallest important element (say, the smallest line of text) as a percentage of the total image height. For ADM, it's expressed as the display's vertical pixel resolution instead, because the concern shifts from font size to individual pixels.

With those three answers in hand, the rest is arithmetic.

Sizing for everyday meeting content (BDM)

The formula, in plain terms

Imagine a presentation slide. If the smallest text on it needs to take up at least 3% of the total image height to stay readable from the back row, that's a 3% EH requirement. AVIXA's formula ties that percentage directly to viewing distance:

Farthest Viewer = Image Height × %EH × 200

Rearranged to solve for what we actually want to know:

Image Height = Farthest Viewer ÷ (%EH × 200)

The constant 200 looks arbitrary, but it isn't — it comes from research into human visual acuity, converted into a usable number so you don't have to redo the underlying trigonometry every time. In practice, we typically test three benchmark values:

Worked example: a 20-person boardroom

Let's put real numbers to it. Say the farthest seat is 6.1 m (610 cm) — about 20 feet (240 inches) — from the display.

(For this content size, the sample presentation slide needs to be divided in two to fit all the content.)

(To go from image height to the diagonal size manufacturers advertise, multiply the height by roughly 2.04 for a standard 16:9 display — that factor comes straight from the Pythagorean theorem applied to a 16:9 rectangle. It works the same whether you're in centimeters or inches.)

The takeaway that surprises most clients

This is exactly why two consultants can look at the same room and recommend two very different screens — it depends entirely on what the client will actually put on it. A room used mainly for video calls and simple slides can comfortably run on a 165 cm (65 in) display. The very same room, if it's expected to show detailed spreadsheets, really needs something closer to 216–249 cm (85–98 in). Same walls, same furniture, completely different answer — because the room size was never the question that mattered.

Sizing for detail-critical content (ADM)

Some rooms exist for exactly one purpose: letting someone catch the detail that matters. A radiologist reviewing a scan. An engineer checking a CAD drawing. An operator watching a security feed for the one alarm that changes. For these, DISCAS switches to the ADM formula, where resolution enters the calculation directly:

Farthest Viewer = (Image Height × 3438) ÷ Vertical Resolution

Rearranged:

Image Height = (Farthest Viewer × Vertical Resolution) ÷ 3438

Just like 200 for BDM, the constant 3438 comes from human visual acuity research — specifically, it's derived from the fact that a person with normal vision can resolve detail down to about one arcminute of visual angle (roughly 1/3438th of a radian, if you enjoy the trigonometry). You don't need to memorize where it comes from — just trust that AVIXA's vision-science task group already did that work.

Worked example: a small technical review room

A reviewer sits 2.44 m (244 cm) — about 8 feet (96 inches) — from the display, checking detailed drawings on a Full HD (1080p) screen (vertical resolution: 1080 pixels):

Run the same calculation in inches — Image Height = (96 in × 1080) ÷ 3438 ≈ 30.2 in (77 cm) — and you land on exactly the same result. Same formula, same constants, just a different starting unit.

The insight most people get backwards

Here's the part clients find genuinely surprising: if that same client wants 4K (UHD) instead of 1080p, at the same viewing distance, the math doesn't let you shrink the screen. Because now every one of those extra pixels needs to be individually resolvable by the eye, the required image height roughly doubles (4K's 2160 vertical pixels are exactly twice 1080p's, so the required image height scales the same way).

In other words: more resolution doesn't let you use a smaller screen for detailed work — it demands a bigger one, unless your viewers sit closer. This is the opposite of what most people assume ("higher resolution means I can go smaller"), and it's exactly the kind of thing worth getting a professional opinion on before you buy.

Don't forget the closest viewer

DISCAS doesn't just protect the back row — it also defines how close is too close, so front-row viewers aren't straining their necks or sitting so near the screen they can't take in the whole image at once. A commonly used starting guideline is that the closest viewer shouldn't sit much nearer than about 1.5× the image height — roughly the point where looking up at the top of the screen starts to exceed a comfortable viewing angle. That's a useful sanity check, but the precise number depends on the room's seating layout and how high the display is mounted, which is really a room-by-room calculation. It's one of the checks we run as part of a full room design — and for detail-critical (ADM) work, there's no minimum closest-viewer distance at all, since sitting closer only helps.

A quick consultant's checklist

When we size a display for a client, this is roughly the order we work through:

1. Measure the farthest seat. Distance from the display plane to the back-most seat that needs to read the content.
2. Decide BDM or ADM. Will people need the overall picture, or every individual detail?
3. Pick a realistic %EH (BDM) or note the intended resolution (ADM). Base it on the actual content, not a guess.
4. Run the formula. Solve for image height, then convert to the diagonal size you'll shop for.
5. Sanity-check the closest viewer. Make sure the front row isn't uncomfortably close.

FAQ

Sizing a display is only one part of designing a room that actually works for how your team uses it. If you'd like us to calculate the right display size — and the right AV system around it — for your space, get in touch with our team.