Aspect ratios for AI images: which to use for what (GPT Image 2 guide)
The right ratio for posters, social, slides, mobile screens, storyboards, and print — copy-paste table included.
The short answer
Always include an explicit ratio phrase in your GPT Image 2 prompt. Use plain English, not Midjourney flags.
| Use case | Ratio | Drop-in phrase |
|---|---|---|
| Print poster | 2:3 | "2:3 portrait poster" |
| Movie poster | 27:40 | "27:40 portrait, theatrical poster" |
| Instagram feed | 4:5 | "4:5 portrait, social feed" |
| Instagram square | 1:1 | "1:1 square" |
| Instagram Story / Reel | 9:16 | "9:16 vertical, story format" |
| Twitter/X header | 3:1 | "3:1 wide banner" |
| LinkedIn banner | 4:1 | "4:1 wide banner" |
| Mobile app screen | 9:19.5 | "9:19.5 portrait, iPhone screen" |
| Desktop hero | 16:9 | "16:9 landscape" |
| Slide deck | 16:9 | "16:9 slide, presentation format" |
| Wide landscape photo | 3:2 | "3:2 landscape, 35mm frame" |
| Magazine cover | 4:5 | "4:5 portrait, magazine cover" |
| Book cover | 2:3 | "2:3 portrait, book cover proportions" |
| 4-panel storyboard | 16:9 | "16:9 landscape, 2×2 storyboard grid" |
| 3-panel vertical | 3:4 | "3:4 portrait, 3-panel storyboard" |
| Square album art | 1:1 | "1:1 square album cover" |
Why ratio matters more than people think
GPT Image 2 doesn't crop your image after rendering — it composes for the ratio you give it. A poster prompt rendered as 1:1 doesn't get cropped to 2:3; it gets a different, worse composition. Aspect ratio is a brief, not a frame.
The three mistakes
- No ratio at all. Defaults to 1:1. Your "movie poster" comes out square.
- Midjourney flags.
--ar 2:3is ignored by GPT Image 2. Use plain English. - Wrong orientation word. "9:16 landscape" is contradictory. Match the number to the word: 9:16 = portrait/vertical, 16:9 = landscape/horizontal.
Quick decision tree
- Printed? 2:3 portrait or 27:40.
- Phone screen? 9:16 vertical or 9:19.5 portrait.
- Social feed? 4:5 portrait if you want maximum stop-scrolling real estate.
- Slide or hero? 16:9 landscape.
- Album / square poster / icon? 1:1.
Skip the lookup
Depikt's generator infers the right aspect ratio from your idea automatically — "a movie poster" gets 2:3, "an Instagram ad" gets 4:5, "a desktop hero" gets 16:9. You don't have to remember the table.
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