> ## Documentation Index
> Fetch the complete documentation index at: https://docs.chexnik.dev/llms.txt
> Use this file to discover all available pages before exploring further.

# Aspect ratios

> Supported aspect ratios per model.

The `aspect_ratio` field is **required** on every generation request. The supported set depends on the model.

| Aspect ratio  | NanoBanana | NanoBanana 2 / Pro |
| ------------- | :--------: | :----------------: |
| `1:1`         |      ✅     |          ✅         |
| `2:3`         |      ✅     |          ✅         |
| `3:2`         |      ✅     |          ✅         |
| `3:4`         |      ✅     |          ✅         |
| `4:3`         |      ✅     |          ✅         |
| `4:5`         |      ✅     |          ✅         |
| `5:4`         |      ✅     |          ✅         |
| `9:16`        |      ✅     |          ✅         |
| `16:9`        |      ✅     |          ✅         |
| `21:9`        |      ✅     |          ✅         |
| `1:4`         |      ❌     |          ✅         |
| `1:8`         |      ❌     |          ✅         |
| `4:1`         |      ❌     |          ✅         |
| `8:1`         |      ❌     |          ✅         |
| `auto`        |      ❌     |          ✅         |
| `from_prompt` |      ✅     |          ✅         |

## Special values

<ResponseField name="auto" type="string">
  Infer the ratio from the first input image. **Image-to-image only**, and not supported by NanoBanana.
</ResponseField>

<ResponseField name="from_prompt" type="string">
  Let the model choose the ratio based on the prompt.
</ResponseField>

<Warning>
  Passing a ratio that the model doesn't support — for example `auto` or `4:1` to NanoBanana — results in a `422` validation error.
</Warning>