# Aspect ratio

**Source:** https://promtable.com/glossary/aspect-ratio

> Aspect ratio is the width-to-height proportion of a generated image or video, e.g. 1:1, 16:9, or 9:16.

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Aspect ratio is the width-to-height proportion of a generated image or video, e.g. 1:1, 16:9, or 9:16.

Aspect ratio sets the shape of the output frame independent of resolution — 1:1 square, 16:9 widescreen, 9:16 vertical, 4:5 portrait. In image and video models it is usually passed as a flag (Midjourney's --ar 16:9) or as the output dimensions. It matters beyond cropping: models are trained on certain ratios, so an unusual ratio can change composition, subject framing, and even content (a 9:16 prompt tends to produce full-body or stacked compositions; 16:9 favors landscapes and establishing shots). Pick the ratio for the destination — Reels and Stories want 9:16, YouTube and banners 16:9, feeds often 4:5 or 1:1.

## When to use

- Matching a target placement (9:16 Reels/Stories, 16:9 YouTube, 4:5 feed).
- Steering composition — vertical for full-body or stacked subjects, wide for scenes.

## When not to use

- Expecting an exotic ratio to look as clean as common ones; far-from-trained ratios degrade.

## Example

```
Input: Midjourney: "city skyline at dusk --ar 16:9"
Output: A widescreen landscape composition framed for video, not a square crop of one.
```

## Common mistakes

- Generating square then cropping to 9:16 and losing the subject — set the ratio up front.
- Pushing extreme ratios that the model handles poorly.
- Confusing aspect ratio (shape) with resolution (pixel count).

## Related terms

- [outpainting](https://promtable.com/glossary/outpainting)
- [seed](https://promtable.com/glossary/seed)
- [prompt-engineering](https://promtable.com/glossary/prompt-engineering)
- [negative-prompt](https://promtable.com/glossary/negative-prompt)

## Sources

- [Midjourney — aspect ratios](https://docs.midjourney.com/docs/aspect-ratios)

*Last updated: 2026-06-02*
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Original page: https://promtable.com/glossary/aspect-ratio
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