The geometry nobody draws
A 21:9 screen at the same diagonal is about 16 percent shorter than a 16:9 screen. That sounds like a benefit until you put people at the back of the room: the bottom of the image drops below the sight line of anyone sitting behind a laptop, and the top edge floats above the presenter's head.
Case one: 4.2 m ceiling, 7 m deep
We mounted a 110-inch 16:9 at 900 mm from the floor. The bottom edge was visible over the seated row and the top edge stayed below the ceiling track. A 21:9 at the same width would have needed to sit higher, and the far row would have been looking up at a 15-degree angle for an hour. They chose 16:9.
Case two: 3.6 m ceiling, 11 m deep
This room was wide and shallow in depth but long in width. The 21:9 filled the wall without eating the whiteboard, and because the room was long, the extra width helped the back row read a spreadsheet side by side. The lower height also kept the screen under the ceiling projector housing.
The check, in order
- Measure floor to ceiling at the mounting wall.
- Subtract 600 mm for the bottom edge clearance and 300 mm for any ceiling fixture.
- Divide the remainder by the width you can afford. That is your maximum aspect ratio.
- If the result is below 0.5, 21:9 will not work at that width.
One practical note on content
Windows and most conferencing apps handle 21:9 badly by default: shared screens get pillarboxed, and the extra width becomes black bars. Unless the room is designed for side-by-side content, a 16:9 panel with a larger diagonal usually delivers more usable pixels than a wider panel with dead space.