Nano Banana 2.1 9:16: 768x1376, 1536x2752 or 3072x5504 for stories

Google lists Nano Banana 2.1 at 768x1376 for 9:16 at 1K, 1536x2752 at 2K and 3072x5504 at 4K. For a 1080x1920 story cover, generate at 2K, scale by 0.7031 so the width is 1080, and trim the extra 15 px of height.

Sume forwards your ratio and tier to the provider and does not document the exact pixels it returns, so this post uses Google's table. Check width and height on the first file you get back before you build a crop on them.

What are the 9:16 sizes?

Google's table lists the vertical ratio as the mirror of 16:9.

Where does the 15 px come from?

1536 times 0.7031 is 1080, and 2752 times 0.7031 is 1935. The frame is 15 px taller than 1920. Trim it from the bottom if your layout has a caption bar there, or split it between top and bottom for a centered subject.

The 1K frame is only 768 wide, so it needs a 1.41 times upscale to fill a 1080 slot. Use it for storyboards, not final covers.

Does 9:16 work with a reference image?

Yes. On Sume, Nano Banana 2.1 takes reference images in input_references, and the URLs must be public HTTPS. Set aspect_ratio explicitly for a vertical result, because auto on an edit matches the reference's shape. Google's own API allows up to 14 references (read 2026-10-09); Sume's ceiling is the range in the catalog row, which is 10 for this model.

{
  "model": "google/nano-banana-2.1",
  "prompt": "Same jacket, worn on a city street",
  "input_references": [
    {
      "type": "image_url",
      "image_url": {
        "url": "https://example.com/jacket.jpg"
      }
    }
  ],
  "aspect_ratio": "9:16",
  "resolution": "2K"
}

What does it cost on Sume?

Billed price is $0.10 at 1K, $0.15 at 2K and $0.20 at 4K, which is the provider list times 1.25. See the image models docs for the full parameter list. A parameter the row does not list returns 400 unsupported_parameter, so a typo fails loudly instead of being ignored.

Stories and Reels covers hide the top and bottom of the frame behind interface elements, so keep the subject in the middle two thirds. That also makes the 15 px trim harmless, because the crop only touches the outer edge. Put any caption inside the safe area in your editor after the crop, not in the prompt.