TV Size and Viewing Distance

Two different figures answer two different questions, and conflating them is behind most of the confused advice about screen sizes. The viewing-angle recommendations — SMPTE's 30 degrees, THX's 40 — are about immersion: how much of your field of view the picture fills. The pixel-pitch limit is about detail: the distance beyond which you can no longer resolve individual pixels, so a higher resolution stops earning its keep.

People conflate the two and conclude that 4K is pointless. It is only pointless if you sit where a 1080p set would have been fine anyway. Sit at the distance THX suggests and the extra resolution is doing plenty of visible work; sit across the room and it genuinely is not.

A screen is sold by its diagonal, which is why a 55-inch 16:9 television is only about 48 inches wide. That also makes diagonal a poor way to compare different shapes — a 34-inch ultrawide monitor and a 34-inch 16:9 one have quite different amounts of screen, and the ultrawide has considerably less height.

The size most people should buy is larger than the one they do. Working backwards from a typical seating distance to a 40-degree field of view usually produces a number that feels excessive, and almost nobody who buys it regrets going bigger. The commonest complaint after upgrading is the opposite one.

None of this accounts for content. A poor-quality stream at 4K looks worse than a good 1080p source, and compression artefacts become more visible as you sit closer, not less.