31 Shorts thumbnails at 9:16: Nano Banana 2.1 2K is $4.65, 4K is $6.20
YouTube recommends 2160x3840 for Shorts thumbnails and accepts uploads only from Studio on a computer. 31 images are $4.65 at 2K or $6.20 at 4K on Sume.
YouTube's help page recommends 2160 x 3840 pixels and a 9:16 aspect ratio for Shorts thumbnails, with a minimum height of 640 pixels (read 2026-10-09). At 4K, Nano Banana 2.1 on Sume is $0.20 an image, so 31 Shorts thumbnails cost 31 x $0.20 = $6.20. At 2K the price is $0.15 and the total is 31 x $0.15 = $4.65.
Sume's normalized 4K tier is not guaranteed to be exactly 2160 x 3840, so check the output size of one image before you batch.
What YouTube says
The facts below come from YouTube Help. The page also says custom Shorts thumbnails can be added only in YouTube Studio on a computer, and that your account must be verified.
| Item | Value |
|---|---|
| Recommended size for Shorts | 2160 x 3840 pixels |
| Minimum height for Shorts | 640 pixels |
| Aspect ratio for Shorts | 9:16 |
| Formats | JPG or PNG |
| Mobile upload limit (videos) | 2 MB |
| Desktop upload limit | 50 MB |
The cost, tier by tier
The Sume Image API lists 9:16 among its normalized ratios, though a model accepts only the values in its own descriptors, so read supported_parameters first. Sume prices Nano Banana 2.1 at $0.075 for 0.5K, $0.10 for 1K, $0.15 for 2K and $0.20 for 4K.
- 31 at 1K: 31 x $0.10 = $3.10
- 31 at 2K: 31 x $0.15 = $4.65
- 31 at 4K: 31 x $0.20 = $6.20
- Three variants each for a test at 2K: 93 x $0.15 = $13.95
File size and format
YouTube lists JPG and PNG and sets upload limits by device (2 MB on mobile for video thumbnails, 50 MB on desktop). Shorts thumbnails are added from a computer, but check the file size of a 4K PNG against the limit that applies to you, and convert to JPG if it is large. Failed generations are not billed on Sume.
A test set for the same 31 Shorts
To compare options yourself, generate three variants per Short at 2K: 93 images at $0.15 is $13.95. Choose the winning variant by watching how the Short performs in the feed, then use the 4K version of that one only: 31 x $0.20 = $6.20 for the finals, for a total of $20.15.
Keep the prompt text short. A vertical thumbnail has little room for words, and big text at 9:16 should survive being shown at a small size on a phone.
Checking the output size
After the first image, open the file and read its width and height. If the long edge is under 3840, the image will be smaller than the 2160 x 3840 the help page recommends. In that case Sume's image upscale at $0.20 per image is an option, though it costs as much as generating at 4K, so generating at 4K is the simpler route when the model allows it.
Budget the whole job, not just the image step. A realistic plan for 31 Shorts is one 2K variant each to review (31 x $0.15 = $4.65), a rerun of the 8 you reject (8 x $0.15 = $1.20), and 4K finals for the rest (23 x $0.20 = $4.60), which comes to $10.45.
Sources
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