Compress a video to a size you choose
Drop a video and pick a target, or use one of the platform pages below. It stays on your device.
Instant client-side compression · Up to 2 GB per file · Zero server upload
How compressing to a size works
Most compressors ask for a quality and leave you to find out how big the result is. FitSize starts from the size instead. It works out how many bits the whole file can spend, sets aside what the audio needs, and gives what is left to the picture. If that is too little for your resolution, it steps the resolution down a rung until each frame gets enough bits to look reasonable.
It never aims exactly at your target. A small margin is kept back for the container and for the encoder running a little over, so the file lands under the number, not on it.
Why it runs in your browser
The video is read, compressed and saved by your own browser, using the hardware video encoder when it has one and a slower software fallback when it does not. Nothing is uploaded to a server, and you can confirm that in your browser's network panel. The compressing code is only downloaded after you choose a file, so this page loads quickly.
Which size to pick
If you know where the file is going, use that destination's page: it aims for the size the platform will really accept, which for email is smaller than the number on the box. If you only know a number, pick it from the sizes below.
Frequently asked questions about video compression
How do I compress a video to an exact megabyte size?
Drop your video into FitSize and select your target size or enter custom megabytes. FitSize calculates the required video and audio bitrates using the exact duration of the file, ensuring the output matches your required file size without trial and error.
Why is client-side video compression safer than cloud converters?
Unlike traditional cloud upload converters that store your video on third-party servers, FitSize runs 100% in your local browser using W3C WebCodecs and WebAssembly. Zero bytes are uploaded to any server, guaranteeing complete privacy for confidential or personal media.
Does compressing a video degrade its visual clarity or frame rate?
FitSize optimizes the video using hardware-accelerated two-pass encoding. It preserves 60 fps motion smoothness, downscaling resolution only when the target bitrate requires it to prevent compression artifacts.
Which video codecs and container formats are supported?
FitSize accepts MP4, WebM, QuickTime MOV, MKV, and AVI containers, and outputs universally compatible MP4 (H.264/AVC with AAC audio) playable on all modern mobile phones, web browsers, and messaging apps.