Video compression calculators
Three small tools for the arithmetic you do before you encode anything. Each one runs in the page, keeps no data and asks for nothing.
Video file size calculator
Will this clip fit under my limit, and at what bitrate?
Give it a duration and a size ceiling and it returns the bitrate you are allowed to spend, or run it the other way and get the size a bitrate produces.
Video bitrate calculator
What bitrate should I encode at?
Resolution, frame rate, what is actually on screen and which codec you are using, turned into a bitrate range and the megabytes per minute it costs.
Upload time calculator
How long will this take to send, and is compressing first worth it?
Transfer time from a file size and a link speed, plus the before-and-after comparison that tells you whether an encode pays for itself.
Why bother with the arithmetic
Compression has a small number of variables and they are all tied together. Size is bitrate times duration. Bitrate is what carries the picture, so resolution and motion set a floor under it. Anything you cannot fit inside the budget has to come out of one of those three, and there is no fourth option.
That means most compression questions are answerable before you start. A 10 minute video into an 8 MB limit leaves 43 kbps for the picture, once 64 kbps of audio is taken out — which is not enough to hold a picture together at any resolution. No encoder setting rescues that. You trim the clip or you raise the limit, and finding that out in five seconds is better than finding it out after a ten minute encode that produced something unwatchable.
The same goes the other way. If the numbers say your file fits at 1080p with room to spare, you can stop reading advice about codecs and just encode it. Knowing which of those two situations you are in is the entire value of these pages.
Where the numbers come from
The size calculator uses exactly the arithmetic the compressor uses when you give it a target, including the few percent it holds back for container overhead, so the two cannot disagree. The bitrate recommendations are starting points drawn from what ordinary footage needs at each resolution, adjusted for frame rate, content and codec. They are a place to begin, not a measurement of your specific video.
Every page says which unit it is using where it matters. Megabytes and megabits differ by a factor of eight, and a surprising amount of bad compression advice on the internet is just someone who divided by the wrong one.
Elsewhere on the site
- The compressor — the actual tool. FFmpeg compiled to WebAssembly, running in your tab, so the file never leaves your machine.
- Compress to a target size — ten presets from 5 MB to 500 MB, each opening the tool already configured for that ceiling.
- The blog — longer explanations of bitrate, CRF, codec choice and why phone video is so large.