Understanding Video File Sizes

Why is a 1-minute video 50 MB on your phone but only 5 MB after compression? File size is determined by resolution, bitrate, and duration. Understanding how these interact helps you choose the right target when compressing.

The Formula: Bitrate × Duration

File size (in bits) = bitrate × duration. So a 5 Mbps video at 60 seconds = 300 megabits = 37.5 MB. Lower the bitrate to 1 Mbps and you get 7.5 MB. That's the core of compression: reduce bitrate for a smaller file, at the cost of quality.

Resolution's Impact

More pixels = more data. 4K has four times the pixels of 1080p, so it needs roughly four times the bitrate for the same quality. Downscaling to 720p or 480p dramatically reduces the data needed. For many sharing use cases, 720p is plenty—and it halves or quarters the file size compared to 1080p.

Estimating for Your Target

If you need a 25 MB file for a 2-minute video, that's 25 MB ÷ 120 seconds ≈ 1.7 Mbps total (video + audio). Media Shrinker does this math for you—enter your target size and duration, and it calculates the optimal bitrate. The tool shows a quality estimate so you can preview before compressing.