AI Image Generator Custom Size: Exact Pixels

You need a website header at exactly 1200×630 pixels. You open an AI image generator, pick a landscape aspect ratio, or type "1200x630" into the prompt, generate, and download. Then you open the file and it is 2560×1440 — or it crops your subject when you force it to fit.

When choosing an AI image generator custom size workflow, separate four things people usually collapse into one: the model's native output size, the target canvas you ask for, the crop or resize the tool applies, and the actual pixels in the downloaded file. Evidence was collected on 2026-10-13 from official tool pages, Vogoo's own source and UI, and one live browser run. The one failed case is documented below rather than hidden.

Why "custom size" rarely means what you expect

Three different paths appear under the same label. Both pixel-target export and a separate resize can deliver the requested dimensions; an aspect ratio alone cannot.

Aspect ratio sets shape, not pixels

An aspect ratio is a shape, not a size. 16:9 can be 1600×900 or 3200×1800. A landscape preset does not necessarily match your header. For example, 1200×630 reduces to 40:21, not 16:9. A custom aspect ratio describes proportions; it still does not establish the delivered pixel count.

To land on 1200×630 you need real pixel inputs, or a resize step afterward — not just a ratio. If you are converting between shapes, see the aspect ratio calculator.

Custom resolution: what the model actually supports

Typing "1200x630" into a text prompt is a request to the model, not a command to the file exporter. Some tools accept explicit width and height fields; others round your request to the model's supported output sizes.

Leonardo's documented generation API requires width and height to be multiples of 8 — 630 is not — and notes that the returned image can differ from the requested size when upscaling is applied. That is one documented API route, not a statement about every model. The point is general: a model has a native resolution it renders at, and your requested resolution is often an export-time conversion.

The custom dimensions workflow

The reliable order is: set the target canvas with real number inputs, generate at the model's supported native size, and let the export step cover, crop, or resize to the target. Working with custom dimensions this way separates "what the model drew" from "what the file should be."

The failure mode to watch for is the one where the tool accepts your width and height and then hands back different pixels. Changing the prompt alone is unlikely to resolve a file-size mismatch. Check the selected model, export settings, and any preparation warning before retrying.

A real run, with a real failure

On 2026-10-13 we ran Vogoo's text-to-image with the UI model Seedream 5.0 Lite, Exact Pixels → Single → Custom Size at 1200×630, one image. The UI reported "Image generated successfully," then "The image is ready, but exact-size preparation failed. Showing the original result."

The generated image's natural dimensions were 2560×1440. The 1200×630 badge described the requested target, not the actual pixels delivered. The download action produced no browser download within 15 seconds, so no 1200×630 file was obtained.

This is one attempt, not a statement about persistent outages or a root cause. It exists to prove the article's point: a size field and a success message do not guarantee the downloaded pixels.

Setting a specific size in Vogoo

Vogoo's text-to-image exposes Exact Pixels → Single → Custom Size with Width and Height inputs. Our source review shows that Vogoo requests a supported model size or aspect ratio, then prepares the exact-size result when needed using proportional scaling and a centered crop. Exact dimensions describe export processing, not universal native model rendering.

To request a specific size:

1. Open text-to-image and choose Text to Image.
2. Set Exact Pixels → Single, then Custom Size.
3. Enter Width 1200 and Height 630, click Add to select the custom size, and set the number of images to 1.
4. Generate, then inspect the downloaded file before trusting it.

An example prompt (an instruction, not a claimed delivered image):

For help shaping prompts that leave room for the crop, see how to write AI picture generator prompts.

Run one small job and confirm the result before you commit to a batch.

Verify the downloaded pixels

Do not trust the badge or the success message. Check the file itself.

• macOS: select the file, press Cmd+I to open Get Info, and read the Dimensions line under "More Info."
• Windows: right-click the file, choose Properties, open the Details tab, and read Dimensions.

If the downloaded image is larger than your target — as 2560×1440 is versus 1200×630 — export to the exact size with a resizer. Adobe Express's image resizer supports custom sizes as an upload-then-resize-then-download workflow. That is a resize step, not raw generation. If the native image came out smaller than you need, see the image upscaler.

When the size is still wrong

FAQ

Does an aspect ratio set the image dimensions?

No. It sets the shape. 1200×630 needs pixel inputs or a resize step.

Can a text prompt force 1200×630 pixels?

No. Prompt text influences content, not the exporter's output size. Use the width and height fields.

What if the tool accepts width/height but returns different pixels?

Treat the returned file's real dimensions as ground truth. The badge is not the file. Resize to your target, or try again.

Can I use a free AI image generator with custom size?

Check the current tool plan and selected model before generating. Adobe advertises its separate image resizer as free, which can be useful if you already have an image. That does not establish that a generator offers free rendering at your chosen dimensions. Verify the downloaded file whatever route you use.

What if I need a specific size and the tool fails?

Keep the original result, read its real dimensions, and finish with a resize or export step. Record the failure and verify a new output before making a batch. This one attempt does not establish reliability across other models or sessions.

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The lesson of the live test: a 1200×630 field and a "generated successfully" message did not produce a 1200×630 file. Before building a batch of headers or share cards, run one small job in text-to-image, open the downloaded file, and read its dimensions. That single check is the difference between trusting a badge and knowing the pixels you shipped.

Sources

1. Adobe Express — Image Resizer — resize and export as an alternative to raw generation.
2. Leonardo — Create a Generation of Images (API reference) — documented divisibility rules and input/output size differences on this route.

Official pages and the Vogoo UI/source were reviewed on October 13, 2026. The Vogoo observation covers one live attempt; the other tools were reviewed through their documentation, not paid output tests. Features and limits may change.