1080p vs 4K: what you actually gain
Four times the pixels, several times the file, and a difference most screens cannot show you.
4 min read
4K is the number every quality menu pushes you toward. Whether it is worth taking depends on the screen you will watch on and on how much bitrate the encode was given.
The arithmetic of the screen
1080p is 1920 × 1080; 4K is 3840 × 2160. The extra pixels only become visible when the display can show them and your eyes are close enough to resolve them. On a phone, or a laptop at normal viewing distance, that condition is essentially never met.
When 4K earns its size
Two cases, both real: a television you sit reasonably close to, and footage you intend to edit, crop or reframe. Cropping into a 4K frame leaves you with usable 1080p; cropping into 1080p leaves you with mush.
Check the size before you assume
Divide the listed file size by the duration. If the 4K rung is only marginally larger than the 1080p one, the encoder was starved and the extra pixels carry compression artefacts rather than detail. Take the smaller file — you lose nothing and save the storage.