Video Bitrate Calculator
Find the exact bitrate for any target file size and duration
100% private. Your file is processed locally in your browser with WebAssembly — it is never uploaded to a server, stored, or seen by anyone.
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The Video Bitrate Calculator works out the exact target bitrate you need to hit a desired file size for a given video duration, using the formula bitrate (kbps) = file size (kilobits) / duration (seconds). Enter your target size and runtime to get the total bitrate, or work backwards to estimate how large a file a chosen bitrate will produce. It also lets you subtract an audio bitrate to isolate the video-only bitrate you should pass to an encoder like x264, x265, or VP9.
Everything is calculated instantly in your browser with plain JavaScript, so there is no file to upload, no waiting, and nothing leaves your device. Because it is pure math rather than video processing, no ffmpeg.wasm or WebAssembly encoding is involved and the result is exact, not an estimate from a sample. It is built for video editors, YouTubers, and developers who need to fit a clip under a hard size cap such as Discord, email, or a platform upload limit.
Why use this tool
Hit hard size caps precisely
Work backwards from a fixed limit like Discord's 25 MB, an email attachment ceiling, or a course-platform upload cap to the exact bitrate that fits, instead of guessing and re-exporting.
Separates video and audio bitrate
Automatically subtracts your audio bitrate from the total budget so the video bitrate you copy into the encoder is correct, the single most common cause of oversized exports.
Works in both directions
Calculate bitrate from a target size, or flip it to predict the output file size from a chosen bitrate and duration for planning storage and uploads.
Instant, private, and offline-capable
Pure browser-side math means results are immediate, no file ever leaves your device, and the calculator keeps working with no internet connection once loaded.
How to use the Video Bitrate Calculator
Choose your direction
Decide whether you want to find the bitrate from a target file size or estimate the file size from a known bitrate, and select that mode.
Enter the duration
Type your video length in hours, minutes, and seconds so the calculator can divide the size budget across the full runtime.
Enter the size or bitrate
Input your target file size in MB or GB (for example 25 MB for Discord) or, in reverse mode, the bitrate in kbps or Mbps.
Set the audio bitrate
Enter your audio bitrate, such as 128 or 192 kbps AAC, so the tool subtracts it and returns the video-only bitrate your encoder needs.
Copy the result
Read off the calculated video bitrate and paste it into your encoder, FFmpeg command, or export dialog, aiming slightly under the value to stay below a hard size cap.
Popular use cases
- A creator needs to send a 4-minute gameplay clip on Discord's free 25 MB limit and uses the calculator to find the exact bitrate that keeps it just under the cap.
- A YouTuber planning a 10-minute upload checks in reverse whether a 5 Mbps 1080p bitrate produces a file size their slow connection can upload in a reasonable time.
- A developer writing an FFmpeg two-pass script computes the precise -b:v video bitrate for a fixed-size deliverable, subtracting the 128 kbps AAC audio track first.
- An online course author compressing lessons to a strict per-file size budget estimates how many minutes of footage fit at a given bitrate before encoding the whole library.