How do I calculate video bitrate for a target file size?

Multiply the size in megabytes by 8, divide by the duration in seconds, and subtract the audio bitrate. That gives kilobits per second — this tool also removes a couple of per cent for container overhead.

What bitrate should I use for 1080p?

About 6 Mbps for H.264 at 30 fps, or 9 Mbps at 60. H.265 and VP9 reach the same quality at roughly 60 per cent of that, and AV1 at about half.

What are bits per pixel and why do they matter?

Bitrate divided by pixels times frame rate. It makes bitrates comparable across resolutions: 0.1 is comfortable streaming quality for H.264, 0.05 is fine for H.265 or AV1, and below 0.02 anything with motion falls apart.

How long a video fits in 25 MB?

At 1 Mbps video plus 128 kbps audio, a little under three minutes. Enter your own bitrate above — the answer scales inversely, so halving the bitrate doubles the length.

Does a higher bitrate always mean better quality?

Only up to a point. Past roughly 0.3 bits per pixel most viewers cannot tell the difference, and the extra data is spent on noise the encoder is faithfully preserving.

Video Bitrate Calculator

Turn a target file size into a bitrate, a bitrate into a file size, or find how long fits under a cap.

The Video Bitrate Calculator runs entirely in your browser. It is arithmetic only — no video is uploaded or processed.

Open the Video Compressor

About Video Bitrate Calculator

File size, bitrate and duration are one equation with three unknowns, and this calculator rearranges it whichever way you need: the bitrate that lands a clip on a 25 MB limit, the size a chosen bitrate produces, or how many minutes fit under a cap. Audio and container overhead are subtracted properly, because forgetting a 128 kbps audio track is what pushes an upload just over the line. The second half answers the question the number alone cannot — whether that bitrate is actually enough. Bits per pixel is the resolution-independent measure: 6 Mbps looks generous at 1080p and thin at 4K, simply because there are four times as many pixels to pay for.

Features

Bitrate from a target file size, allowing for audio and overhead
File size from a bitrate, in MB, MiB and GB
Maximum clip length under a size cap
Presets for common limits such as Discord, email and DVD
Bits per pixel, the resolution-independent quality measure
Recommended bitrates by resolution, frame rate and codec
H.264, H.265, VP9 and AV1 efficiency factors
Ready-to-paste ffmpeg bitrate flags

How to use the Video Bitrate Calculator

Pick whether you know the size, the bitrate or neither
Enter the clip duration as seconds, m:ss or h:mm:ss
Choose the audio bitrate you are encoding at
Check bits per pixel against your resolution before committing to the encode

Example

Input

25 MB target · 5:00 duration · 128 kbps audio

Output

Video bitrate: 526 kbps
-b:v 526k -b:a 128k

A five-minute clip inside a 25 MB mail limit leaves about half a megabit for video — fine for a screen recording, thin for sport.

Common errors & troubleshooting

The encode comes out larger than the target. — Audio and container overhead were probably left out. Both are subtracted here, and a couple of per cent is reserved for muxing, which is roughly what MP4 costs.
The file is the right size but looks blocky. — Check bits per pixel. Below about 0.02 for H.264 the encoder cannot keep up with motion, and the answer is a lower resolution or frame rate rather than a bigger number.
A two-pass encode misses the target slightly. — That is normal — rate control aims for an average, and the first pass has to guess. Leaving three to five per cent of headroom is more reliable than trying to hit the cap exactly.

Frequently asked questions

How do I calculate video bitrate for a target file size?: Multiply the size in megabytes by 8, divide by the duration in seconds, and subtract the audio bitrate. That gives kilobits per second — this tool also removes a couple of per cent for container overhead.
What bitrate should I use for 1080p?: About 6 Mbps for H.264 at 30 fps, or 9 Mbps at 60. H.265 and VP9 reach the same quality at roughly 60 per cent of that, and AV1 at about half.
What are bits per pixel and why do they matter?: Bitrate divided by pixels times frame rate. It makes bitrates comparable across resolutions: 0.1 is comfortable streaming quality for H.264, 0.05 is fine for H.265 or AV1, and below 0.02 anything with motion falls apart.
How long a video fits in 25 MB?: At 1 Mbps video plus 128 kbps audio, a little under three minutes. Enter your own bitrate above — the answer scales inversely, so halving the bitrate doubles the length.
Does a higher bitrate always mean better quality?: Only up to a point. Past roughly 0.3 bits per pixel most viewers cannot tell the difference, and the extra data is spent on noise the encoder is faithfully preserving.

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