Everything above runs the trigonometry forwards: a screen and a distance give a field of view and a sharpness. This runs it the other way, which is the question people actually have. Set the viewing distance above and read the three sizes off here.
Pixels per inch describes the screen alone. Pixels per degree is what reaches your eye, and it doubles when you sit twice as far away.
20/20 vision resolves one arcminute. A degree holds 60, so one pixel per arcminute is 60 pixels per degree: where a pixel grid becomes an image.
20/10 vision needs about 120 PPD before pixels vanish: twice the density or twice the distance. Plenty of people are nearer 20/30 without knowing.
SMPTE (30°) and THX (about 40°) are about immersion, not sharpness. Check both; they pull in opposite directions.
Once PPD is past your limit, more pixels change nothing you can see. That is why 8K is a hard sell in an average living room: at normal seating you would need a wall-sized screen before the extra pixels became visible at all.
This page models resolvable detail only. Contrast ratio, black level, colour volume and motion handling frequently matter more to how good a picture looks: a high-contrast 1080p panel routinely beats a washed-out 4K one.
Two screens sharing a diagonal can differ by a quarter in usable area if their aspect ratios differ, which is why a 16:9 and a 4:3 of the same nominal size are not the same screen. Viewing-distance figures are comfort guidance drawn from typical acuity, not a standard, and they say nothing about your eyes.
A 60 PPD limit is for 20/20 vision. At 20/40 the limit is 30 PPD, at 20/10 it is 120, so the television genuinely is sharper to some people in the room than to others.
PPI is a property of the screen alone. PPD is what your eye receives, because it also accounts for viewing distance. A phone at 460 PPI held at 12 inches delivers about 96 PPD, and a 4K television at 80 PPI viewed from 8 feet about 134. Both are past the 60 that 20/20 vision resolves, which is why both look perfectly sharp despite a nearly six-fold difference in PPI.
Because at typical living-room distances both already exceed what your eye can resolve. A 55-inch screen from 8 feet gives about 67 PPD at 1080p — already past the roughly 60 PPD that normal vision distinguishes. The 4K version delivers 134 PPD, but that extra detail lands below your eye's resolving limit. Move closer or buy a bigger screen and the difference appears.
20/20 vision is defined as resolving detail subtending one minute of arc. A degree contains 60 arcminutes, so one pixel per arcminute is 60 pixels per degree. That is about 30 cycles per degree of alternating light and dark lines, which matches the measured contrast-sensitivity limit of the healthy eye.
Substantially. 20/10 vision resolves detail half the angular size, so it needs about 120 PPD before pixels disappear — twice the pixel density, or twice the viewing distance, of someone with 20/20. Plenty of people also sit below 20/20 without realising, which is why the same screen genuinely looks different to different viewers.
SMPTE recommends the screen fill at least 30° of your horizontal field of view for cinema content; THX recommends up to about 40° for a more immersive picture. Both are about immersion rather than resolution — you can satisfy them and still be too far to resolve every pixel, or sit inside them and see the pixel structure.
Releases in which this page changed, newest last. Derived from the archived copy of every release, not from notes written afterwards — so it reflects what actually shipped. Site-wide passes are left out; they are in the full changelog.