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What is video resolution
Resolution is just the number of tiny squares, called pixels, that make up each frame of a video. A 1080p video has 1920 pixels across and 1080 pixels down, while 480p only has 854 by 480. More pixels mean more information has to be stored and sent through the internet.
Think of pixels like small tiles on a wall. A wall with more tiles looks clearer, but it also takes longer to build and needs more material. Same with video; lower resolution means fewer pixels to send, so it uses less data.
Fewer pixels mean less data, and video stretching happens to fit the screen
Sometimes people think a low-resolution video uses more data if it is played on a big screen, because it looks stretched. That is not true. The stretching happens on your device, not through your internet connection.
Your TV, phone, or computer just makes the small image fit the screen by filling in extra pixels locally. It may not look as sharp, but it does not download any extra data.
Other things that also affect data use: Bitrate, frame rate, and compression
Resolution is the biggest factor, but not the only one. Bitrate, frame rate, and compression can also change how much data a video needs.
1. Bitrate
Bitrate means how much data is sent every second. A higher bitrate usually gives a cleaner image, but it also uses more data. This is why a 720p video with very high bitrate might still use more data than a 1080p video that is well compressed.
2. Frame rate (FPS)
Frame rate is how many pictures are shown per second. A 60-fps video can use about twice as much data as a 30-fps one because it has more frames.
3. Codec (compression)
The compression method, called a codec, matters too. Newer ones like H.265 or AV1 can make files smaller without losing much quality, so they can save data compared to older types like H.264.
How much data different resolutions might use
Here is a rough guess of how much data you might use per minute when playing videos from the internet—these are just estimates, since they depend on bitrate and compression.
- 144p might use around 1–1.5 MB per minute
- 480p might use around 8–15 MB per minute
- 720p might use around 20–45 MB per minute
- 1080p might use around 50–70 MB per minute
- 4K can go over 300 MB per minute
If you want to save data, lowering the resolution is the easiest way. Your device will stretch it to fit the screen, but that does not use more data. Resolution mostly decides how many pixels need to be sent, while bitrate, frame rate, and codec just fine-tune how that data is handled.
So yes, lower resolution videos use less data because they simply have less to send.
Source: Reddit discussion (ELI5. Why do lower resolution videos use less data?)