How do I find the bitrate for a target file size?

Convert the target size to bits, divide by the duration in seconds, then divide by 1000 to get the total kbps. Subtract the audio bitrate to get the video bitrate. This tool does all of that for you.

Why subtract the audio bitrate from the total?

The container holds both streams, so total bitrate = video + audio. To keep the file at your target size you give the video only what is left after the audio bitrate.

Does it use MB as 1000 or 1024 KB?

It treats MB and GB as binary units (1 MB = 1024 × 1024 bytes, 1 GB = 1024 × 1024 × 1024 bytes), which matches how media file sizes usually display.

What if I leave the audio bitrate at zero?

Then the full total bitrate is assigned to video. Set a realistic audio bitrate (often 128–320 kbps) so the video figure reflects what is actually left.

Is this for one-pass or two-pass encoding?

It gives you the average bitrate to target, which is exactly what two-pass (target-bitrate) encoding needs to hit a precise file size. One-pass constant-quality encoding does not use a fixed bitrate.

Why is my calculated video bitrate negative or zero?

Your audio bitrate is larger than the total bitrate the target size allows. Either raise the target size, shorten nothing you can, or lower the audio bitrate.

Is anything uploaded?

No. The calculation runs entirely in your browser and no files or data are sent anywhere.

Bitrate Calculator (Audio + Video)

Bitrate calculator for audio and video

Plan an encode by working backwards from a target file size. Enter the size you want, the clip duration and the audio bitrate, and the tool returns the total bitrate plus the video bitrate to set — ideal for two-pass encoding to a disc, an upload limit or a streaming budget.

How it works

The target size is converted to bytes (MB and GB are treated as binary units), then to bits by multiplying by 8. Dividing by the total duration in seconds and by 1000 gives the total bitrate in kbps:

total kbps = (size in bytes × 8) ÷ 1000 ÷ duration in seconds

The video bitrate is then the total minus the audio bitrate you entered, since the file must hold both streams.

Example

Fit 700 MB into a 90-minute clip with 128 kbps audio:

Size = 700 × 1024 × 1024 = 734,003,200 bytes → 5,872,025,600 bits
Duration = 90 × 60 = 5400 seconds
Total = 5,872,025,600 ÷ 1000 ÷ 5400 ≈ 1087.4 kbps
Video = 1087.4 − 128 ≈ 959.4 kbps

Target	Duration	Audio	Total	Video
700 MB	90 min	128 kbps	≈1087 kbps	≈959 kbps

Everything runs locally in your browser — no files or data leave your device.