Video Compressor Calculator
Find the exact video bitrate that makes a video fit a size limit. Enter the length and the target size, set the audio bitrate and a safety margin, and the calculator shows the video bitrate, the total bitrate and a two-pass FFmpeg command. Add the resolution and frame rate to see whether that bitrate is enough for a good picture with H.264, H.265, VP9 or AV1.
- Runs in your browser
- No sign-up
- Free to use
Minutes:seconds or hours:minutes:seconds, e.g. 3:30 or 1:02:15.
0 for a video without sound. 96–128 kbps AAC is fine for speech and most music.
MP4 headers and bitrate variation; 2–5% keeps the file under the limit.
The bitrate is exact arithmetic; the quality rating is a rule of thumb, since the result also depends on how much movement and detail the video contains.
How to use Video Compressor Calculator
- Enter the video length and target file size.
- Set the audio bitrate and safety margin.
- Optionally add resolution, frame rate and codec.
- Use the bitrate or the FFmpeg command in your encoder.
Video Compressor Calculator features
Exact arithmetic
Size × 8 ÷ duration, minus audio and overhead.
MB or MiB
Decimal and binary megabytes.
Quality estimate
Bits per pixel per frame against typical values per codec.
Resolution hint
Suggests a smaller frame size when the bitrate is too low.
FFmpeg command
Two-pass encode that hits the size accurately.
Formula shown
Every step of the calculation.
When to use Video Compressor Calculator
- Fitting a clip under an upload or attachment limit.
- Planning bitrates for a batch of videos.
- Choosing between resolutions for a fixed size.
- Understanding why a compressed video looks blocky.
Video Compressor Calculator FAQ
How is the bitrate calculated?
The target size in bits is reduced by the overhead percentage and divided by the duration in seconds. The audio bitrate is subtracted to leave the video bitrate.
Why a safety margin?
Encoders vary the bitrate from second to second and the container adds headers. A margin of 2–5% keeps the final file under the limit.
What is bits per pixel?
The bitrate divided by width × height × frame rate. It shows how much data each pixel gets; H.264 typically needs around 0.1 for good quality, newer codecs less.
Why two-pass encoding?
The first pass analyses the video, the second distributes the bitrate where it is needed and reaches the target size closely.
MB or MiB?
Upload limits are usually in MB (1,000,000 bytes); some programs show MiB (1,048,576 bytes).
Is anything uploaded?
No. It is a calculator; no video is needed.
Bitrate and file size
A video file’s size is almost exactly its bitrate multiplied by its duration. That makes it possible to work backwards: if a platform accepts files up to a certain size, the maximum bitrate follows from the length of the video. Audio takes its share first, and a small part goes to the container.
Whether that bitrate looks good depends on how many pixels it has to describe. The same 2 Mbps that looks clean at 1280 × 720 can look blocky at 1920 × 1080 with fast motion. Bits per pixel per frame is a simple way to compare, and the calculator rates it against typical values for each codec.
Newer codecs need fewer bits for the same quality: H.265 and VP9 roughly 30–40% fewer than H.264, AV1 up to about half. They take longer to encode and are not supported everywhere, so H.264 remains the safe choice for maximum compatibility.
When the bitrate is too low, reducing the resolution or frame rate usually looks better than squeezing more pixels into too few bits. The calculator suggests a frame size that would reach acceptable quality at the available bitrate.