Aspect Ratio Calculator

Compute the matching dimension for a target aspect ratio. Includes presets for 16:9 / 4:3 / 21:9 / 1:1 / 9:16.

Width (px)

Height (px)

16:9

Common Resolution Presets

Name	Width	Height	Ratio

Popular uses

Calculate 16:9 and 9:16 sizesPlan social resolutionsAvoid bars and padding

Next tools

SNS Video Resizer Crop Video Tool Thumbnail Extractor

What this tool does

Width ↔ height calculator
Common-ratio presets
Even-number correction for H.264

How to use

1

Pick a ratio

Preset or custom.
2

Enter width or height

The other side calculates automatically.
3

Copy the result

Paste straight into ffmpeg.

What each setting means

Aspect ratio

Width:height ratio (e.g. 16:9).

Width / Height

One drives the other.

Recommended settings

YouTube / TV

16:9 (1920×1080)

Global standard.

TikTok / Reels / Shorts

9:16 (1080×1920)

Vertical SNS standard.

Cinematic

21:9 (2560×1080)

Cinemascope-like framing.

Common pitfalls

Symptom: H.264 encode fails

Cause: Odd resolution.

Fix: Use scale=-2:720 to force even.

Equivalent FFmpeg commands

Reference commands you can run on the desktop FFmpeg CLI.

Historical log: 2026-09-11, 2 successful example executions and 0 excluded (desktop FFmpeg 8.1, fixtures). This log does not verify later edits, browser controls or visual quality.

Keep width, set height to 720

ffmpeg -i input.mp4 -vf scale=-2:720 -c:v libx264 -crf 23 output.mp4

Force exact resolution

ffmpeg -i input.mp4 -vf scale=1280:720,setsar=1:1 output.mp4

Browser support & limits

Calculator only — apply via another tool.

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 even resolution?

H.264 / H.265 use 4:2:0 chroma subsampling, which requires even dimensions.

21:9 vs 2.35:1?

Similar, not identical. 21:9 ≈ 2.33:1; 2.35:1 is true cinemascope.