VID-02

Display Size (AVIXA DISCAS)

ANSI/AVIXA V202.01 · ANSI/AVIXA V201.01 · ANSI/AVIXA D401.01

01 · Method

Sizing methodⓘ

02 · Room geometry

Farthest viewer distanceⓘ

Closest viewer distance

Height to bottom of imageⓘ

Seated eye heightⓘ

03 · Image format

Aspect ratio

Source resolutionⓘ

Awaiting input7 fields left: Sizing method · Farthest viewer distance · Closest viewer distance · Height to bottom of image · Seated eye height · Aspect ratio · Source resolution

Drawing

The drawing appears when the inputs are complete

01
Size a display or projected image from the farthest viewer using the DISCAS Basic Decision Making and Analytical Decision Making methods, with closest-viewer and sightline checks.
02
Tip. BDM and ADM answer different questions. BDM asks whether the smallest element is readable, so it needs the element height; ADM asks whether individual pixels are resolvable, so it needs the source resolution. Use ADM only where pixel-level detail genuinely drives the decision — medical imagery, CAD, control-room video — or it will oversize the display.
03
200 — BDM acuity factor
04
3438 — ADM acuity factor
05
1 arc-min — Visual acuity limit
06
2 : 1 — Closest viewer minimum

AVIXA DISCAS standard overview

DISCAS — Display Image Size for 2D Content in Audiovisual Systems — is the ANSI/AVIXA standard for sizing a display from viewing distance and content type. It replaces judgement about "how big does the screen need to be" with two defined methods, each answering a different question about what the farthest viewer must be able to resolve.

Basic Decision Making (BDM)

For content where the viewer must take in the information but not every fine detail. Sized from the smallest element that has to stay legible, expressed as a percentage of image height.

Use cases

Presentations and slide content
Word processing and spreadsheets
Classrooms and training rooms
Boardrooms and conference rooms
Information and wayfinding displays

Formula

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

Acuity factor 200

Analytical Decision Making (ADM)

For specialist viewing where pixel-level detail drives the decision. Sized from source resolution so that every pixel subtends at least one arc-minute at the back row — the limit of human visual acuity.

Use cases

Medical imagery — X-ray, MRI, CT
Engineering and CAD drawings
Architectural plans and schematics
Forensic and evidence review
Photographic evaluation

Formula

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

Acuity factor 3438 (arc-minutes per radian)

Legacy 4/6/8 rule: before DISCAS, designers divided the farthest viewing distance by 6 for general content or 4 for detailed content. Those ratios ignore both the element size and the source resolution, and DISCAS supersedes them. This tool implements DISCAS, not the legacy rule.