How to use Video File Size Calculator

Enter the video bitrate (kbps or Mbps) you plan to encode at.
Add the audio bitrate (or pick a preset; leave blank for no audio) and the duration.
Adjust container overhead if needed (2% default). The estimated size and its video/audio/overhead breakdown update live.

Video File Size Calculator

Before you kick off a long export or plan storage for a batch, you want to know roughly how big the output will be. File size comes down to one estimate:

size (bytes) ≈ (video bitrate + audio bitrate) × duration ÷ 8 × (1 + overhead)

This tool computes it with the audio track and container overhead included — the parts a back-of-envelope "video bitrate × time" usually forgets.

The parts that make up a file

Video is almost all of it. At 5 Mbps, one minute is 5,000,000 × 60 ÷ 8 = 37.5 MB.
Audio is a smaller, steady addition. A 192 kbps AAC track is 192,000 × 60 ÷ 8 = 1.44 MB per minute — easy to overlook, but it adds up over a long runtime.
Container overhead is the wrapper (MP4/MKV/MOV): headers, the index, per-frame metadata. Usually 1–3%; the tool defaults to 2%.

The breakdown under the result shows each part so you can see where the bytes go.

When you'd reach for this

Planning an encode. Pick a target bitrate and see the resulting size before committing to a 40-minute export.
Fitting an upload limit. If a platform caps uploads at, say, 2 GB, work backwards: lower the bitrate until the estimate fits, then check quality.
Estimating storage. Multiply the per-clip estimate across a batch to size a bucket or disk.
Sanity-checking a bill. Egress and CDN costs track bytes served; a size estimate is the first input.

Why the real file differs

The estimate assumes an average bitrate held across the whole clip. Real encodes rarely do that:

VBR (variable bitrate) spends more on motion and detail, less on static shots. Two-pass VBR targets an average and lands close; single-pass can drift.
CRF / constant-quality modes don't target a bitrate at all — they hold quality and let size float. For those, this tool is a planning estimate only.
Keyframe interval and scene cuts nudge size, since keyframes cost more than predicted frames.

Treat the number as a solid estimate — typically within a few percent for CBR and two-pass VBR — not a precise promise.

Decimal units

Everything here is decimal/SI: 1 MB = 1,000,000 bytes, 1 Mbps = 1,000,000 bits/second. That matches how encoders and platforms quote numbers. If your operating system reports binary units (MiB/GiB), expect the file to read about 5% smaller at gigabyte scale — same bytes, different labels.

To go the other direction — from a target size to the bitrate that fits it — use the Video Bitrate Calculator. For live-streaming upload targets and platform caps, see the Streaming Bitrate Calculator.

Frequently asked questions

How do I estimate a video file's size before encoding?

Add the video and audio bitrates, multiply by the duration in seconds, divide by 8 to get bytes, then add a few percent for container overhead. This tool does exactly that — enter video bitrate, audio bitrate, and length, and it returns the estimated MB/GB with a video/audio/overhead breakdown.

Why include audio bitrate separately?

Because audio is a real, constant chunk of the file that pure "video bitrate × time" math ignores. A 192 kbps AAC track over 10 minutes is about 14 MB on its own — small next to video, but not nothing, and it's the difference between an estimate that's close and one that's under.

What is container overhead and why 2%?

The container (MP4, MKV, MOV) adds structure around the raw streams — headers, an index/moov atom, per-frame metadata. That's typically ~1–3% on top of the media payload, so 2% is a reasonable default. Fragmented or heavily-chaptered files can run higher.

Why is my real file a bit different from the estimate?

Variable-bitrate (VBR) encoding spends more bits on complex scenes and fewer on simple ones, so the average drifts from the target. Two-pass VBR lands close to the target; constant-quality (CRF) modes ignore a target bitrate entirely, so use this as a planning estimate, not a guarantee.

Are these megabytes decimal or binary?

Decimal (SI) — 1 MB = 1,000,000 bytes, matching bitrate math. Your OS may show binary MiB (1,048,576 bytes), which reads about 5% smaller at the GB scale.