Bitrate calculator
Calculate the approximate bitrate from a target file size and duration (target size + duration in, bitrate out) — useful when setting an export size limit such as an upload cap.
Result
Required total bitrate
Video bitrate after audio
How to use this tool
- Enter your target file size.
- Enter the video or audio's duration.
- Enter the audio bitrate your export uses (0 for silent video or an audio-only file).
- Read the total bitrate, and the video bitrate to type into your editor's export settings.
Assumptions
- Assumes the export uses a constant bitrate — a variable-bitrate export may end up somewhat above or below the target size.
Technical details: what the fields mean
- Target file size
fileSizeMb - The file size you're aiming for, in decimal megabytes (1 GB = 1000 MB).
- Duration
durationMinutes - Length of the video or audio. 1m 30s = 1.5.
- Audio bitrate (0 if none)
audioKbps - The audio track's bitrate. 128 kbps is a common default for AAC; check your export preset.
Methodology
Average bitrate (Mbps) = target file size (decimal MB) × 8 ÷ duration (seconds). This reverses the file-size estimate: choose size and duration to find the average bitrate, not a guaranteed encoder setting.
Worked example
100MB target, 5-minute video with 128 kbps audio
Inputs: Target file size: 100 MB, Duration: 5 minutes, Audio bitrate (0 if none): 128 kbps
Result: 2.67 Mbps total; set video to about 2539 kbps.
Fitting a 2-minute clip under a 25 MB attachment limit
Inputs: Target file size: 25 MB, Duration: 2 minutes, Audio bitrate (0 if none): 128 kbps
Result: 1.67 Mbps total, about 1539 kbps video. Aim a little lower, e.g. 1400 kbps, to leave room for overhead.
A 2-hour film in 8 GB
Inputs: Target file size: 8000 MB, Duration: 120 minutes, Audio bitrate (0 if none): 0 kbps
Result: 8.89 Mbps average for everything in the file.
Practical guidance
- Aim slightly under your actual size limit, since container/format overhead and variable-bitrate encoding can push the real file a little above a constant-bitrate calculation.
- For a strict size limit, two-pass encoding with an average bitrate lands closer to the target than a single pass.
- If the video bitrate comes out very low for the resolution, reduce the resolution or frame rate rather than accept a blocky picture.
Common mistakes
- Setting the exact calculated bitrate with no margin, then finding the exported file is slightly over the target due to format overhead or a variable-bitrate encoder.
FAQs
What bitrate do I need for a 100MB, 5-minute video?
About 2.67 Mbps in total — roughly 2539 kbps for the video if the audio is 128 kbps.
Why is my exported file bigger than the target?
The container adds a little overhead, and variable-bitrate encoders can overshoot. Leave a 5–10% margin below a hard limit.
Is MB the same as Mb here?
No. File size is in megabytes (MB); bitrate is in megabits per second (Mbps). There are 8 bits in a byte, which is why the formula multiplies by 8.
Last reviewed: 2026-10-11
An average-bitrate estimate. Codec, audio, container and metadata overhead consume part of the target size; variable-bitrate exports may also finish above or below it.
This tool provides an indicative estimate, based on the assumptions stated above.
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