Key takeaways
- Scaling both sides by a factor changes the pixel count by its square: 3840 × 2160 at 50% is 1920 × 1080 and 25.0% of the original.
- Bitrate needed for similar quality roughly follows the pixel count, which is why a half-size video can be a quarter of the size.
Scale and bitrate
Scaling is applied to both sides, so a 50% scale gives a quarter of the pixels. Encoders spend bits roughly in proportion to pixels at similar quality, so the bitrate hint in the results is a guide, not a promise.
Scale down for a smaller file; avoid scaling up, which adds no detail. Whole-number factors such as 50% give the cleanest result because every output pixel comes from the same number of source pixels.
Scenarios
| Scenario | Scaled resolution | Pixel count change |
|---|---|---|
| 4K to 50% | 1920 × 1080 | 25.0% of the original |
| 4K to 75% | 2880 × 1620 | 56.3% of the original |
| 1080p to 50% | 960 × 540 | 25.0% of the original |
| 1080p to 66.67% | 1280 × 720 | 44.4% of the original |
| 1080p to 150% | 2880 × 1620 | 225.0% of the original |
| Phone vertical to 50% | 540 × 960 | 25.0% of the original |
Scale ladder for 1080p and 4K
| Scale | 1080p becomes | Share of the pixels | 4K becomes | Share of the pixels |
|---|---|---|---|---|
| 100% | 1920 × 1080 | 100.0% of the original | 3840 × 2160 | 100.0% of the original |
| 75% | 1440 × 810 | 56.3% of the original | 2880 × 1620 | 56.3% of the original |
| 66.67% | 1280 × 720 | 44.4% of the original | 2560 × 1440 | 44.4% of the original |
| 50% | 960 × 540 | 25.0% of the original | 1920 × 1080 | 25.0% of the original |
| 33.33% | 640 × 360 | 11.1% of the original | 1280 × 720 | 11.1% of the original |
| 25% | 480 × 270 | 6.3% of the original | 960 × 540 | 6.3% of the original |
Both sides shrink by the scale, so the pixel count falls by its square: half the size is a quarter of the pixels.