Bluesky’s official post creation guide sets two limits that matter when you resize: a post can hold up to four images, and each image is limited to 2 megabytes in size. The guide does not prescribe a required pixel size. The practical job is therefore to keep each file under the 2 MB byte cap while preserving the image’s proportions, and to check the result before you post.
The limits Bluesky sets for images
The table below separates what the official guide states from what it leaves open. Most resizing confusion comes from treating the open items as if they were rules.
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| Item | What the official guide says | Source |
|---|---|---|
| Images per post | Up to four | Bluesky post creation guide |
| File size per image | Limited to 2 megabytes | Bluesky post creation guide |
| Alt text | Each image can have its own alt text | Bluesky post creation guide |
| Pixel dimensions | An aspect-ratio width/height hint is shown; no universal pixel size is prescribed | Bluesky post creation guide |
| Metadata | Bluesky recommends stripping image metadata before upload; the guide says the server may become stricter about blocking metadata in the future | Bluesky post creation guide |
The guide does not display a publication date for this passage, so treat its wording as current as of the time you read it and check the page itself if you need to cite it.
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Megabytes and pixels are different limits
The 2 MB rule is a byte limit on the uploaded file. Pixel dimensions, which are the width and height of the image in pixels, control how the picture is framed and displayed. Changing one does not automatically change the other in a predictable way. A large-dimension photo saved with heavy compression can fall under 2 MB, while a smaller image saved with little compression can still exceed it.
This is why “resize to a Bluesky size” is an ambiguous instruction. If your image is rejected for being too large, you need to reduce its file size. If your image is cropped or displayed in an unexpected shape, you need to adjust its proportions or framing. Those are separate fixes.
How to resize without distorting the image
Scaling an image should keep its width-to-height ratio. Stretching it to fit a shape you prefer makes people and objects look wrong, and it is the most common visible mistake in resized social images. If you want a different shape, make a deliberate choice:
- Decide the goal. Either the file must fit under 2 MB, or the composition must change. Do not treat these as one task.
- Keep the original proportions. In your editor, lock the aspect ratio before you change the width or height.
- Crop for a new shape. If you need a different frame, crop the image so the subject stays inside it, rather than stretching the full picture.
- Add canvas space only when you need padding. If you want the whole image visible in a different shape, extend the background instead of distorting the photo.
How to export and check the file size
Once the image is the size and shape you want, export it and confirm the file is within the cap. The steps below are practical editorial guidance; the official guide establishes the 2 MB limit but does not specify a compression setting or reduction order.
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- Check the file size. On Windows, right-click the file and open Properties. On macOS, select the file in Finder and press Command+I. Confirm the size is 2 MB or less.
- If it is too large, reduce dimensions first. Lower the width and height in small steps while keeping the aspect ratio locked, then export again.
- If you need more reduction, lower the export quality. Use a moderate setting and check the result.
- Inspect the image at full size. Look for blocky edges in skies, smeared text, or halos around high-contrast areas. If you see them, the compression went too far; return to a slightly larger export.
Preparing each image before you post
Run through this checklist for every image in the post:
- No more than four images in one post.
- Each file is 2 MB or smaller.
- Proportions are preserved, or any crop was chosen on purpose.
- Alt text is written for that specific image. Each image has its own field.
- Image metadata is removed before upload, as Bluesky recommends.
Tools for resizing
Two widely used tools are described below using only their own published help and product pages. This article does not report side-by-side tests of their output quality or speed, and neither page says anything about Bluesky specifically.
Adobe Express
Adobe’s help page for its Resize image Quick action, last updated April 28, 2026, says the tool accepts JPEG, JPG, PNG, WebP, or HEIC files up to 40 MB. It offers aspect-ratio presets and custom pixel width and height, and lets you download the result. The 40 MB figure is the tool’s input limit. It does not describe the size of the file you can export, and it is not Bluesky’s limit.
Canva
Canva’s image resizer page says you can upload a photo, choose preset or custom dimensions, and download the result as JPG or PNG. It is a sensible choice if you also want to edit text or add design elements before posting. The page does not state an input file-size limit, and it does not promise that an export will fall below 2 MB. Check the file size yourself after every export.
| Comparison point | Adobe Express | Canva |
|---|---|---|
| Dimension controls | Aspect-ratio presets and custom pixel width and height | Preset or custom dimensions |
| Input formats | JPEG, JPG, PNG, WebP, HEIC | Not stated on the cited page |
| Input size limit | 40 MB | Not stated on the cited page |
| Download formats | Not stated on the cited help page | JPG or PNG |
| Bluesky-specific preset | Not stated | Not stated |
| Source date | Help page last updated April 28, 2026 | No publication date displayed |
Choose between them based on the controls you need and whether you want editing features. Neither page establishes which one produces better results for Bluesky posts.
Quick Recap
Troubleshooting common problems
- The upload is rejected for size. The problem is almost certainly the file size in bytes, not the pixel dimensions. Check the file properties, then reduce dimensions or export quality as described above.
- The image looks cropped or shifted. The framing changed when the shape changed. Re-export with a deliberate crop or added canvas instead of relying on automatic fitting.
- The image looks soft or blocky after reduction. The export was compressed too far. Use a larger dimension or a higher quality setting, then recheck the file size.
- A tool’s limits or options differ from this article. Tool features, format support, and caps change. Consult the tool’s current help page.
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