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Glossary · metric

What is Resolution + pixel density?

Resolution is the pixel count of a video frame (1920×1080 = "1080p"). Pixel density is pixels per inch on a display. The two interact: 1080p video on a 24-inch monitor (~92 ppi) looks visibly less sharp than the same 1080p video on a phone (~400 ppi). The right download resolution depends on the display you'll watch it on.

Also called:pixel density · ppi · dpi

See [/glossary/resolution](/glossary/resolution) for the basics. This entry covers the resolution-vs-display interaction.

Pixel density matters because the human eye has a limit on resolvable detail per arc-minute of visual angle. Roughly 60 pixels per degree of vision is the limit; closer viewing distances or higher pixel density helps; further viewing distances waste resolution.

Concrete: an iPhone 15 at typical viewing distance (10-12 inches) shows ~400 ppi which exceeds eye resolving power. A 1080p video on this phone is mostly indistinguishable from 4K — the extra pixels are wasted. A 65-inch 4K TV at typical living-room distance (8 feet) shows ~33 ppi; the eye can resolve every pixel, so 4K matters here.

Practical rule: for phone viewing, 720p is sufficient; for laptop, 1080p; for TV, 4K is justified if the screen is 50"+. For everything else, smaller download = same perceived quality.

Common questions

Why does 720p look sharp on my phone but blurry on my laptop?
Pixel density. Your phone packs ~400 ppi; your laptop screen ~150 ppi. The same 720p file is more pixels-per-inch on the phone, looking sharper. On the laptop the same file is spread across larger physical pixels, looking less detailed.

Related terms

Resolution

Resolution is the pixel count of a video frame, expressed as width × height.

FPS (frames per second)

FPS (frames per second) is the number of distinct still images displayed per second of video.

Aspect ratio

Aspect ratio is the proportion of a video frame's width to its height.

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