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Calculator

Video File Size Calculator

Estimate the final file size of your video before encoding. Select resolution, format, quality level and duration for a rough first estimate.

Medium — Good quality, balanced size
10 minutes

Estimated File Size

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💡 Note: this is a rough estimate. The bitrate for each resolution and quality level is this site's own rule of thumb, not an official standard. The real size depends on your encoder settings and on the content itself.

How the estimate is calculated

File size is bitrate multiplied by duration. Bitrate is measured in bits per second and file size in bytes, so you divide by 8:

size (MB) = bitrate (kbps) × duration (seconds) ÷ 8 ÷ 1000

The calculator starts from a base video bitrate for each resolution (720p 3,500 kbps; 1080p 6,000 kbps; 1440p 12,000 kbps; 4K 25,000 kbps), then adjusts it for the quality level and format you pick. These base values are our own assumptions for a typical H.264 upload, not measured or official figures. For comparison, YouTube recommends 8 Mbps for a 1080p upload at 24–30 fps and 12 Mbps at 48–60 fps (YouTube recommended upload encoding settings, checked 24 October 2026).

Worked example you can check by hand

1080p, MP4 (H.264), Medium quality, 10 minutes:

bitrate  = 6,000 kbps (1080p base × 1.0 for Medium)
duration = 10 × 60 = 600 s
size     = 6,000 × 600 ÷ 8 ÷ 1000 = 450 MB  (about 0.45 GB)

That covers the video only. Audio adds its own bitrate in the same way: 192 kbps of AAC over 600 s is 192 × 600 ÷ 8 ÷ 1000 ≈ 14 MB.

Does the formula match a real encode?

We encoded a 20-second 1080p test clip with FFmpeg 8.1.2 at a fixed target bitrate (24 October 2026):

ffmpeg -i src1080.mp4 -c:v libx264 -b:v 6000k -maxrate 6000k -bufsize 12000k -c:a aac -b:a 192k out-6000k.mp4

Formula: (6,000 + 192) kbps × 20 s ÷ 8 = 15,480,000 bytes, about 15.5 MB. Across two runs, the files were 15,694,741 and 15,669,600 bytes, about 15.7 MB, roughly 1.2–1.4% larger than the formula. ffprobe measured the video at about 6,066–6,076 kbps and the audio at about 192 kbps, and the MP4 container adds a little overhead. The formula only holds this well when you encode to a target bitrate. With CRF (quality-based) encoding, FFmpeg doesn't aim for a size, so the same CRF can give very different sizes for different content.

Working backwards from a size limit? Rearrange the formula: bitrate (kbps) = size (MB) × 1000 × 8 ÷ duration (s). For example, a 100 MB limit for a 5-minute (300 s) video gives 100 × 8000 ÷ 300 ≈ 2,667 kbps in total for video and audio together.