VidKit

Free tool · No upload

Video bitrate calculator

Enter a target file size and how long your clip is, and this works out the exact bitrate the video can use to land on that size — plus the highest resolution that still looks good. The same math VidKit's compressor uses, on its own so you can plan before you encode.

MB
Clip length min sec

How the math works

File size is just bitrate multiplied by time. Flip that around and the bitrate you can afford is the target size (converted from bytes to bits — multiply by 8) divided by the clip's length in seconds. Whatever the audio track uses comes off the top first, and a small slice goes to container overhead — the index tables and headers an MP4 needs to be seekable. What's left is your video bitrate.

Bitrate alone doesn't tell you how good it looks — that depends on how many pixels it has to cover. The telling number is bits per pixel: video bitrate divided by (width × height × frame rate). Above roughly 0.1 the picture stays crisp; below about 0.045 H.264 starts to smear. That's why this calculator recommends a resolution instead of just handing you a number: 2 Mbps is plenty for 480p, tight for 720p, and soft for 1080p. When a bitrate is too low for a resolution, dropping to the next size down looks better than keeping the resolution and starving it of data.

A note on units: this uses decimal megabytes (1 MB = 1,000,000 bytes), the same way upload limits are usually quoted. If you need to hit a limit exactly, aim a little under — email attachments in particular add about a third in encoding overhead. Not sure which platform allows what? See our video upload size limits reference.

Ready to compress?

This tells you the target; VidKit hits it for you. The compressor takes a size in MB, works out this exact bitrate, picks the right resolution automatically, and checks the result lands under the limit — all in your browser, nothing uploaded.

Frequently asked questions

What bitrate do I need for Discord's 10 MB limit?
It depends entirely on length. A 1-minute clip with audio gets about 1.2 Mbps of video — enough for a clean 360p and borderline 480p. Stretch that same 10 MB across 5 minutes and there's only room for low-resolution, visibly compressed video. Put your real numbers in above for the exact figure, or just compress to 10 MB and let VidKit pick the bitrate and resolution for you.
Should I lower the bitrate or the resolution to fit?
Lower the resolution. A bitrate that's fine for 720p becomes blocky if you force it to cover a full 1080p frame — the same data spread over more pixels. Dropping to a resolution the bitrate can actually feed almost always looks better. The calculator's recommendation already does this for you.
Does higher frame rate need more bitrate?
Yes — 60 fps has twice as many frames to encode as 30 fps, so it needs roughly twice the bitrate for the same sharpness. If you're fighting a tight size limit and the footage isn't fast motion, 30 fps buys you a lot. Switch the frame rate above to see the effect.
Is this the same bitrate VidKit will actually use?
Very close. VidKit's compressor uses this same budget arithmetic — audio first, container overhead, then video — and then verifies the finished file and nudges the bitrate down if the first pass came out slightly over. The calculator gives you the plan; the compressor guarantees the result.
Why decimal MB and not 1024-based?
Because that's how upload limits are almost always quoted — Discord's "10 MB", Gmail's "25 MB" and so on mean decimal megabytes. Using the same convention means the number you calculate here matches the limit you're aiming at. If a specific tool uses binary (MiB), you'll have a little extra headroom, not less.

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