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 16:9.

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

With a start frame

The API does not reconcile aspect_ratio with the image you pass in image_inputs. Supplying a 16:9 still while asking for a portrait ratio gives the model contradictory instructions. Match them — see Flux image to video.

Models covered on this page

• FLUX Pro