The Complete Guide to Aspect Ratios in AI Image Generation
Why Aspect Ratio Matters
Aspect ratio isn't just a technical setting — it shapes composition. A portrait-oriented image (9:16) creates a very different visual flow than a cinematic widescreen (21:9), even with an identical prompt. Choosing the right ratio before you generate saves significant time in post-processing.
Every Ratio, Explained
Square (1:1)
Best for: Instagram posts, profile pictures, app icons, print-on-demand products The most versatile format. Square compositions work well across almost all social platforms and force balanced, centered subject matter.
Landscape (16:9)
Best for: YouTube thumbnails, website hero banners, presentation slides, desktop wallpapers The standard widescreen format. Gives subjects room to breathe and works naturally with horizontal storytelling.
Portrait (9:16)
Best for: Instagram Reels, TikTok, Pinterest, mobile wallpapers, Stories content Vertical-native format that dominates mobile-first social platforms. Works especially well for portraits and tall architectural subjects.
Classic Photo (4:3 and 3:4)
Best for: Traditional photography compositions, digital photo albums, tablet screens 4:3 mirrors the classic DSLR crop ratio. Familiar and balanced, well-suited for editorial and editorial-style content.
Cinema (21:9)
Best for: Ultra-wide monitor wallpapers, film-style headers, panoramic landscapes Extremely wide format that creates an inherently dramatic, cinematic feel. Ideal for landscape and architectural photography styles.
Standard Portrait (2:3 and 3:2)
Best for: Print photography, magazine covers, physical prints 2:3 is the standard 4×6 print ratio — use it whenever the image will be physically printed.
Social-Optimized (4:5)
Best for: Instagram feed posts optimized for maximum vertical space 4:5 takes up the most screen real estate in Instagram feeds without triggering portrait-only formatting.
Quick Reference Card
| Platform | Recommended Ratio |
|---|---|
| Instagram Post | 1:1 or 4:5 |
| Instagram Reels/TikTok | 9:16 |
| YouTube Thumbnail | 16:9 |
| Pinterest Pin | 2:3 |
| Twitter/X Header | 3:1 |
| LinkedIn Banner | 4:1 |
| Desktop Wallpaper | 16:9 or 21:9 |
| Print (4×6") | 2:3 |
| Website Hero | 16:9 |
The "Auto" Setting
When you're unsure which ratio suits your prompt, use Auto. Nano Banana 2 will analyze your prompt and select the most compositionally appropriate ratio — portrait for tall subjects, wide for landscapes, square for balanced compositions.
Pro Tip: Match Ratio to Subject
Tall subjects (people, trees, buildings) → portrait ratios (9:16, 2:3) Wide subjects (landscapes, cityscapes, groups) → landscape ratios (16:9, 21:9) Balanced subjects (products, single objects) → square or near-square (1:1, 4:5)