Free tool
Video size calculator file size from length and bitrate.
Length times bitrate, done properly. Presets for phones, YouTube and ProRes, and the reverse: the bitrate that lands under a size limit.
File size from bitrate
610 MB
Bitrate for a target size
2.5 Mbps
Compress video will hit that target for you: pick Target size and the number.
Megabytes are decimal, one million bytes, the way phones and platforms count.
Video size calculator at a glance
content.win estimates video size, free, with presets from 720p to 4K.
- Works with
- Length, resolution, frame rate and codec, or a bitrate.
- Comes back as
- An estimate of the file size, with presets from 720p to 4K.
- Runs
- In your browser.
- Limits
- No limit.
- Price
- Free. No account.
The formula
Everything else is a preset for this one line.
- Size in bytes = (video bitrate + audio bitrate, in bits per second) × seconds ÷ 8.
- So 8 Mbps video plus 128 kbps audio for 10 minutes: 8,128,000 × 600 ÷ 8 = 609,600,000 bytes, about 610 MB.
- Resolution and frame rate don't appear in the formula. They only matter through the bitrate a given quality needs, which is what the presets encode.
What changes the size
- Bitrate
- The only number that directly sets size. Double it, double the file. Everything below is a reason to need more or less of it.
- Resolution
- 4K has four times the pixels of 1080p and needs roughly two to four times the bitrate for the same look, not four, because larger frames compress more efficiently.
- Frame rate
- 60 fps needs about 50 percent more than 30 fps, not double, for the same reason.
- Codec
- HEVC needs about half the bitrate of H.264 for the same quality; AV1 about a third. ProRes is deliberately huge: it's made for editing, not delivery.
- Motion and detail
- Talking heads and slides compress far below the preset; sport, confetti, water and fast pans blow past it. Variable bitrate encoders adapt, which is why real files miss the estimate by 10 to 20 percent.
- Audio
- Small next to video. 128 kbps AAC is a megabyte a minute; uncompressed stereo is 11.
Questions people ask
How do I calculate video file size?
Add the video and audio bitrates, multiply by the length in seconds, divide by eight to turn bits into bytes. A 10-minute video at 8 megabits a second with 128 kilobit audio is about 610 megabytes. The calculator does this as you type.
Why is my real file a different size?
Most encoders use variable bitrate, so the average lands above or below the number you set depending on how much movement there is. Talking heads come in under; sport, confetti and screen scrolling come in over. Treat the estimate as plus or minus 15 percent.
Which bitrate should I use for YouTube?
YouTube's own upload guide: 8 megabits a second for 1080p at 30 frames, 12 for 1080p60, 16 for 1440p, 35 to 45 for 4K30 and 53 to 68 for 4K60. Add about a quarter for HDR. Uploading higher doesn't hurt; YouTube re-encodes everything.
How much smaller is HEVC (H.265) than H.264?
Around 40 to 50 percent at the same visual quality, which is why phones default to it. AV1 saves another 20 to 30 percent over HEVC but is slower to encode. The presets here are the bitrates each codec needs for the same look.
How big is one minute of 4K video?
From a phone in HEVC, about 170 megabytes at 30 frames and 400 at 60. As a YouTube-grade H.264 export, about 300 megabytes. In ProRes 422 HQ, close to 6 gigabytes.
What's the difference between MB and MiB?
A megabyte here is one million bytes, the way platforms, phones and drive makers count. Windows shows mebibytes, 1,048,576 bytes each, and labels them MB, so its numbers read about 5 percent smaller for the same file.
What bitrate gets a video under a size limit?
Use the second calculator: enter the limit and the length and it gives the bitrate. Or skip the maths and use the Compress video tool with a target size; it works out the same numbers and encodes the file.