What Bitrate Do I Need for This Video?

Size over time, and that's it

A megabyte is eight megabits. So a target file size is a budget of bits, and dividing it by the running time gives the bits per second you're allowed to spend.

500 MB for a ten-minute video is 4,000,000 kilobits over 600 seconds — 6,667 kbps.

Now take the audio out

This is the step that gets skipped, and it's the whole reason the tool exists.

Your encoder asks for a video bitrate. If you hand it the 6,667 you just worked out, the finished file overshoots by exactly the size of the audio track — because the audio spends the same budget.

With a 128 kbps stereo track, the number to actually type in is 6,539.

That's why both figures are shown side by side: the total the file can afford, and the video bitrate to set.

When it matters, and when it doesn't

At 500 MB the audio takes 1.92% of the budget. You could ignore it and nobody would notice.

Now squeeze the same ten minutes into 25 MB:

Target	Total budget	Audio share	Video bitrate
500 MB	6,667 kbps	1.92%	6,539
25 MB	333 kbps	38.4%	205

Same audio track, same video. At a tight target it's taking close to two fifths of everything you have.

Push further and the audio alone exceeds the budget — a 60-minute video into 1 MB reports a negative video bitrate and an audio share of 5,760%. That's the honest answer rather than a fabricated small positive number, and it tells you what to fix: cut the audio bitrate, or accept a bigger file.

Why your file browser disagrees

You'll encode a 500 MB file and Windows will call it 477 MB. Nothing went wrong.

This tool uses decimal megabytes — a million bytes — which is what cameras, video tools and upload limits mean. Windows reports mebibytes (1,048,576 bytes) and labels those MB too.

Two different units sharing a name. Our file size converter shows both readings of the same byte count if you need to check one against the other.

Will the encoder actually hit it?

Depends on the mode:

• Two-pass or explicit target-size — lands within about a percent. It measures the content first, then spends the budget.
• Single-pass VBR — looser, but usually close.
• Constant quality (CRF) — ignores your target completely. It gives you whatever size the content needs to reach the quality you asked for.

CRF is the better choice when you have no hard limit, and the wrong one when you do.

Add roughly a percent for container overhead — muxing, headers, index data. If the ceiling is genuinely hard, treat the result as a maximum and take a few percent off.

Why resolution isn't an input

Because it doesn't change the arithmetic. Bitrate decides how big the file is; resolution, frame rate and how much movement is in the shot decide how good it looks at that size.

A static screen recording and a fast-moving sport at the same bitrate and resolution are not comparable — one has almost nothing changing between frames, the other has everything changing.

So "what bitrate do I need for 1080p" isn't a calculation. Encode a difficult thirty seconds at two candidate bitrates, look at them, then use the arithmetic to confirm the whole video fits.

Running it backwards

The last two outputs take a bitrate you already know you like and tell you what it produces.

At 5,000 kbps with the same 128 kbps audio, ten minutes comes to 384.6 MB — and 13.0 minutes of video would fit inside a 500 MB target.

That second figure answers a question the forward direction can't: not does this video fit, but how much video fits. Useful when you're deciding what to cut, or how long a recording can run before it breaks a limit.