GPT Image aspect ratios for a Pinterest pin (2:3) and Instagram (4:5)

For a Pinterest pin, request aspect_ratio: "2:3"; for an Instagram portrait post, request 4:5. Both are among the 17 normalized ratios Sume's image docs list. Whether a given model accepts them is decided by its catalog row, so read supported_parameters before you pin a ratio.

Adobe's September 2026 Firefly post announces 10 aspect ratios for GPT Image 2; that is Firefly's list. Pinterest's product specs recommend 2:3, or 1000 x 1500 pixels. Sume facts are from the image docs, read 2026-10-01.

Which ratios does Sume list?

The normalized aspect_ratio values are 1:1, 16:9, 9:16, 4:3, 3:4, 3:2, 2:3, 4:5, 5:4, 1:2, 2:1, 1:4, 4:1, 1:8, 8:1, 9:21 and 21:9, or auto for the provider to choose. That is 17 ratios.

Can ChatGPT Image 2.5 hit 1000 x 1500 exactly?

Not with those numbers. openai/gpt-image-2.5 takes image_size as a named preset, auto, or custom pixels where both edges are multiples of 16, the longest edge is at most 3840, the ratio is at most 3:1 and the total is 655,360 to 8,294,400 pixels. 1000 is not a multiple of 16, but 1024 x 1536 is, and it is exactly 2:3. The model also takes up to 16 reference images.

How do I get exactly 1080 x 1350 for Instagram?

The docs are cautious here. They say Banana Pro sends 4:5 at a native size near 928 x 1152 at 1K, and that exact 1080 x 1350 is a post-step. Plan to resize or crop afterward rather than assuming the generator returns those pixels; see AI image at Instagram 4:5.

What if a model rejects my ratio?

A model only accepts the values its catalog descriptors list. Check the model's supported_parameters, and on edit calls prefer aspect_ratio: "auto" to match the reference image (omitting the field is not the same as auto).