File Size Estimator

Estimate output file size from CRF, resolution, codec and duration before you encode.

Resolution

Codec

Duration (seconds)

CRF Value (23) — lower = higher quality & larger file

18 (high quality)23 (default)32 (low quality)

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⚠ CRF is content-adaptive, so actual file size varies significantly based on content complexity (motion, noise, gradients, etc.). This estimate is approximate only.

Popular uses

Estimate file size before postingCompare CRF and bitrate optionsPlan storage needs

Next tools

Video Compressor Bitrate Calculator Discord Video Compressor

What this tool does

H.264 / H.265 coefficients
Try several CRF / resolution combos
No actual encode required

How to use

1
Enter duration
Seconds or HH:MM:SS.
2
Pick codec / resolution / CRF
Use a preset or custom values.
3
Read the estimate
Approximate MB output.

What each setting means

Resolution

Vertical pixels.

CRF

Quality target — lower means bigger files.

Codec

H.265 ≈ 1.5× more efficient than H.264.

Recommended settings

YouTube CRF 23 1080p

~10min ≈ 100–500MB

Varies with source complexity.

Discord 10MB

720p · CRF 28–30

Aggressive compression.

Common pitfalls

Symptom: Estimate doesn't match reality

Cause: CRF varies with scene complexity.

Fix: Treat ±30% as expected error.

Equivalent FFmpeg commands

Reference commands you can run on the desktop FFmpeg CLI.

Encode and check

ffmpeg -i input.mp4 -c:v libx264 -crf 23 -preset fast output.mp4

Then ls -lh output.mp4

Browser support & limits

Estimates only (±30%)
AV1 / VP9 less accurate

Privacy

This tool only does math in your browser. Inputs stay on your device — nothing is uploaded. Read the privacy policy →

Frequently asked questions

Why not exact?

CRF is a quality target, not a bitrate. Real bitrate depends on the content.

H.264 or H.265?

Same quality, H.265 is ~30–50% smaller. Use H.264 for max compatibility.