What aspect ratio should I use for Instagram AI images?

4:5 portrait (1080×1350) for feed posts, because it takes up the most screen space. Use 9:16 (1080×1920) for Stories and Reels.

How do I change the aspect ratio in Midjourney?

Add --ar followed by the ratio to the end of your prompt, for example --ar 9:16 for a phone wallpaper or --ar 16:9 for a widescreen image.

Can I make a square AI image wider without cropping?

Not by resizing — that stretches it. Some generators can extend an image outward (often called outpainting or zoom out). Otherwise, regenerate with the ratio you need.

AI Images6 min read·November 14, 2026

AI Image Sizes and Aspect Ratios, Explained

Most AI images come out square. Most places you want to put them are not. An Instagram portrait post, a YouTube thumbnail, a phone wallpaper and an A4 print all want different shapes. Asking for the right shape when you generate saves you from cropping off the part you liked.

What each generator gives you by default

Midjourney makes square images unless you add the --ar parameter, for example --ar 16:9 or --ar 4:5. It accepts almost any ratio, so pick the one your destination uses.

ChatGPT (DALL·E 3) offers three sizes: 1024×1024 square, 1792×1024 wide and 1024×1792 tall. The newer GPT image model offers 1024×1024, 1536×1024 and 1024×1536. Ask for "a wide image" or "a tall image" in plain words.

Stable Diffusion XL is trained around 1024×1024 and works best at sizes with about the same pixel count, such as 1216×832 or 832×1216. Very different sizes tend to produce doubled subjects or stretched compositions.

Gemini and other chat-based generators accept a ratio in the prompt, such as "in 16:9". Sizes change as models update, so treat these numbers as a starting point and check the output.

Tip: Writing prompts for several generators? PromptItIn’s AI image prompt builder adds the right ratio syntax for the generator you pick.

Pick the ratio for where the image is going

Instagram feed: 4:5 portrait (1080×1350) takes the most screen space; 1:1 also works. Stories and Reels: 9:16 (1080×1920).

YouTube thumbnail: 16:9 (1280×720). Website hero or banner: 16:9 or wider, such as 21:9. Phone wallpaper: 9:16 or taller.

Print: A4 and A3 paper are about 1:1.41, close to 5:7. Generate at 2:3 or 3:4 and trim a little, or generate square and place it on the page with a border.

Already generated it in the wrong shape?

Crop it to the ratio you need with ImageSmith’s crop tool — it has 1:1, 4:5, 9:16 and 16:9 presets and runs on your phone.

Then resize to the exact pixels the platform wants. Uploading at the right size means the platform recompresses less, so the image stays sharper.

For print, the A4 print tool places one or more images on a page and exports a PDF.

Tip: Need the image bigger rather than a different shape? Resizing up adds pixels but not detail. Regenerate with an upscale option in your generator instead.

Crop your AI image to any ratio

Square, portrait, story or widescreen presets. Free, and your image never leaves your device.

Open the crop tool

Set the aspect ratio in the prompt and the image arrives ready to use. When it does not, a crop and a resize fix it in under a minute — without uploading your image anywhere.

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