Flux aspect ratio options: what it accepts and what it rejects

Flux Pro v1.1 accepts 5 aspect ratios through the API:

• 16:9
• 9:16
• 1:1
• 4:3
• 3:4

That is the widest set on the platform — every ratio the API supports at all.

It does not affect price

Aspect ratio is free. Flux Pro v1.1 costs 5 credits ($0.05–$0.07) at any of the ratios above.

Default

Omit aspect_ratio and you get 1:1.

-d '{"model":"flux-pro","prompt":"...","aspect_ratio":"3:4"}'

With a reference image

This is an image-generation model, not an image-to-video model. The adapter passes the first image_inputs URL upstream; it does not crop a reference to the requested output ratio or guarantee reference fidelity. Review the reference-image integration guide and inspect the resulting still at its intended crop.

Continue with models and parameters

• Flux API key: two paths, and what changes after you have one
• Flux API parameters: every accepted value and what it costs
• Flux resolution options and what they cost
• Browse all models and parameters guides

Models covered on this page

• FLUX Pro