100 viewing-distance cells — how close you must sit for 4K to matter
Screen width and height, two recommended distances, and the distance at which pixels become visible — for every meeting of 20 screen sizes and 5 resolutions. One diagonal is enough; the rest follows.
55" · Where pixels become visible
- HD (1280×720)327 cm
- FHD (1920×1080)218 cm
- QHD (2560×1440)163.5 cm
- 4K UHD (3840×2160)109 cm
- 8K (7680×4320)54.5 cm
The diagonal decides the rest
A screen is sold by its diagonal alone. At 16:9 that fixes the rest: width is 0.8716 of the diagonal, height 0.4903. A 55-inch set is therefore 121.8 cm wide and 68.5 cm tall. The width grows more slowly than the inch number suggests, because the diagonal is √(width² + height²).
The recommended distance is an angle
The standard is not “so many metres” but “how much of your field of view the screen fills”. SMPTE says 30 degrees, THX up to 40. A wider angle means sitting closer, so the THX distance is always shorter — and the ratio between them is a constant 1.36, whatever the screen size. For 55 inches: 227 cm and 167 cm.
One arcminute decides where pixels show
Normal 20/20 vision is defined as resolving one arcminute, a sixtieth of a degree. A pixel smaller than that blends into its neighbour. Working out the distance at which one pixel spans an arcminute gives the line where the grid starts to show: 109 cm for 4K on a 55-inch screen, 218 cm for FHD. Twice the pixel density halves the line.
So when does 4K actually earn its keep
For extra resolution to reach your eye, you have to sit close enough to resolve the pixels of the resolution one step below. Farther than that, the lower resolution already looks smooth and nothing changes. This turns up something neat: at the SMPTE distance, FHD pixels sit exactly on the threshold — the recommended distance is only 4 % beyond the pixel limit. The ratio holds for every screen size, because both quantities scale with screen width.
Living rooms are usually farther than that
A sofa two and a half to three metres from the screen is common. The pixel limit for 4K on a 55-inch set is 109 cm, so from that seat 4K and the resolution below it look the same. There are two ways out: sit closer, or keep the distance and go bigger — a larger screen has larger pixels, which pushes the limit farther out.
Find it by size and resolution
SMPTE distance (30°)
HD (1280×720)
FHD (1920×1080)
QHD (2560×1440)
4K UHD (3840×2160)
8K (7680×4320)
How to read this
- Width = diagonal × 0.8716, height = diagonal × 0.4903 (16:9).
- Recommended distance = screen width ÷ 2 ÷ tan(angle/2). SMPTE 30°, THX 40°.
- Pixels become visible at pixel size ÷ tan(one arcminute).
- For this resolution to matter, sit inside the pixel limit of the step below.
Frequently asked questions
Q. How far should I sit from a 55-inch TV?
227 cm by SMPTE, 167 cm by THX. If you want the screen to fill your view like a cinema, THX is the closer figure.
Q. Why does 4K not look as different as expected?
Distance. The pixels of a 55-inch 4K set only separate closer than 109 cm. From a sofa 2.5 m away it is indistinguishable from the resolution below.
Q. How do I get more from the same seat?
Go bigger. A larger screen has larger pixels, which pushes the distance at which you can resolve them farther out.
Q. Is 8K worth it?
It depends where you sit. Even a 98-inch 8K set has a pixel limit of 97 cm; beyond that it does not separate from 4K.
Q. What does this calculation assume?
A 16:9 screen and 20/20 vision, defined as resolving one arcminute. Sharper eyes see pixels from farther away.