> ## Documentation Index
> Fetch the complete documentation index at: https://docs.bananahub.io/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`       |      ✅     |          ✅         |

## Special values

<ResponseField name="auto" type="string">
  The service picks a concrete ratio for you: a ratio named in the prompt (e.g. `16:9`) wins; otherwise it snaps to the closest ratio to your first input image; otherwise (text-to-image with no ratio in the prompt) it defaults to `9:16`. Supported on all models — for NanoBanana the result is always one of its supported ratios.
</ResponseField>

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