The Magic Image Size Prompt for ChatGPT – Is there one?

My Question for ChatGPT:  When creating an image through ChatGPT, I can never get an aspect ratio of 12:6 or 12:7 (for Social posting) for images such as 1200×600 or 1200×650 or something similar. They’re always a 9:16 or 16:9 ratio or 1X1. What is the prompt that I should be using to get a different aspect ratio such as 16:7, 16:6, or something other than 16:9?  Is it even possible?  I want different image sizes for Social Postings.

When it comes to social media, the right image size can significantly impact engagement. For example, a visually appealing post with an optimal image size can lead to higher shares and likes. It’s essential to consider how images display across different platforms, as each has its own recommended dimensions. For instance, a well-crafted image for Instagram might not suit Facebook or Twitter.

ChatGPT response:  There isn’t a “magic prompt” for image sizes that reliably forces 1200×600, 1200×650, 16:7, 16:6, etc. in ChatGPT—because the image generator is usually constrained to a small set of fixed output canvases, and prompts can’t override those hard limits. Understanding the constraints of the image size will help in crafting better prompts.

Understanding the limitations of AI-generated images is crucial for optimizing prompts. This knowledge can help you better tailor your requests to achieve the desired image size. Users have reported varying success with different formats, often depending on trial and error. Documenting your findings when trying different prompts can also lead to better results in the future.

• In the Open AI Images API, the size must be one of a few allowed values (e.g., 1024x1024, 1536x1024, 1024x1536, or model-specific sets). Experimenting with different image sizes may yield varied results.

  Experimentation is key with the Open AI Images API. Users might find that certain combinations of sizes produce superior outcomes. For instance, an image generated at 1536x1024 might work well for a Facebook post, while 1024x1536 could be more suitable for a Pinterest pin.

• For DALL·E 3, the allowed sizes are likewise limited (historically 1024×1024, 1792×1024, 1024×1792).
  So if the UI/underlying model is locked to those, it will ignore “make it 1200×650” no matter how strongly you say it.

  Learning from past experiences can help refine your prompts. Observing how different sizes perform on various platforms can guide future image requests. If an image fails to attract attention, consider adjusting the prompt for improved results.

The practical workaround that does work

Generate in the closest supported landscape size, then crop/resize to your exact pixel dimensions.
To make that painless, you “prompt for the crop” (composition), not for the final pixels.

This approach not only saves time but also ensures that you maximize the potential of your generated images. By focusing on composition first, you can maintain control over the aesthetic quality of your visuals.

Copy/paste prompt template (works well)

Replace the bracketed parts:

PROMPT

Create a wide landscape illustration in [STYLE].
Composition must be safe for a final crop to [TARGET PIXELS] ([TARGET RATIO]).
Keep all important elements and any text inside a centered safe zone: 80% width × 70% height.
Leave extra “breathing room” at the top and bottom (sky/negative space) so cropping won’t cut anything off.
No borders, no frames, no letterboxing.

This template can also be modified for different styles or themes, allowing for greater flexibility in your image generation process. For example, if you’re aiming for a minimalistic design, you can adjust the style in the prompt accordingly.

Example for 1200×650 (≈1.846:1):

Create a wide landscape illustration in WebWize Illustrative style.
Composition must be safe for a final crop to 1200×650 (aspect ratio ≈ 1.846:1).
Keep all important elements and any text inside a centered safe zone: 80% width × 70% height.
Leave extra breathing room at the top and bottom so cropping won’t cut anything off.
No borders, no frames, no letterboxing.

In practice, users often find that providing context or specifying the elements to include in your prompt leads to better results. For example, if creating an image for a blog post about travel, specifying landmarks or themes can enhance the image’s relevance.

Why this works

Even if the generator outputs something like 1792×1024 (near “landscape”), your layout is built to survive the crop to your exact banner size afterward.

Utilizing this strategy can empower content creators to ensure their visuals align with the brand’s aesthetic and message. Moreover, it fosters a more cohesive visual strategy across all marketing materials.

Quick crop math (so you can be consistent)

Consistency in image size can also enhance brand recognition. When followers see visually cohesive content, they are more likely to associate it with your brand. This principle applies not only to social media but also to websites and marketing materials.

If you generate 1792×1024 (common for “wide/landscape” in some systems), then:

• Target 1200×600 (2:1) ⇒ crop height to 1792 / 2 = 896 (trim top+bottom), then resize to 1200×600

• Target 1200×650 (1.846:1) ⇒ crop height to 1792 / 1.846 ≈ 971

• Target 1200×640 (1.875:1) ⇒ crop height to 1792 / 1.875 ≈ 956

  Understanding the math behind cropping can also lead to more strategic image selections. For instance, knowing how to calculate dimensions can help ensure that the final product fits seamlessly into the intended space.

• Target 1200×700 (1.714:1) ⇒ keep height 1024 and crop width to 1024 × 1.714 ≈ 1755

If you do have access to a “Size” selector (best case)

Incorporating a “Size” selector into your workflow can drastically improve the efficiency of generating images. This selector allows quick adjustments to the final output, ensuring that the image fits the required specifications without additional editing.

Use it. The “size”/canvas setting is the thing that actually controls dimensions in supported workflows.
Then use the prompt above to make the composition crop-safe

By understanding the backend settings of the image generation tool you are using, you can leverage its full potential. Exploring additional features or settings could reveal opportunities for even better results.