In most cases you do not: a 1080 px wide image at 4:5 or 1:1, exported as JPG or PNG under 1 MB, fits both Threads and Bluesky without a second version. The differences worth planning for are Bluesky's much smaller file limit, the number of images each post can hold, and how much text sits next to the image.
Neither app publishes a recommended pixel size or a feed crop rule for images, so the table below separates what each platform documents from what we recommend. Facts were checked on October 5, 2026, on Meta's and Bluesky's own pages.
What image specs do Threads and Bluesky publish?
Threads specs come from Meta's Threads API documentation, which is written for apps that publish to Threads; the Instagram Help Center pages for Threads describe features but give no image dimensions. Bluesky specs come from its developer docs and the record schemas (lexicons) in its official atproto repository. X is added for comparison.
| Spec | Threads | Bluesky | X |
|---|---|---|---|
| Image formats | JPEG and PNG officially supported | Any image type accepted by the schema | GIF, JPEG, PNG (Help Center) |
| Max file size per image | 8 MB | 1,000,000 or 2,000,000 bytes (see below) | 5 MB |
| Width | 320 to 1440 px; scaled up or down to fit | Not published | Not published in the Help Center |
| Aspect ratio | Up to 10:1 | No limit published; each image stores its ratio | 2:1 to 3:4 shown in full |
| Images per post | Carousel of 2 to 20 items | 4 in the original image embed, up to 10 in the app since June 2026 | 4 (API docs) |
| Post text | 500 characters | 300 graphemes | Not covered here |
| Alt text | Supported and editable | A field on every image in the schema | Up to 1,000 characters (Help Center) |
| Color | Converted to sRGB | Not published | Not published |
Where do Bluesky's own pages disagree?
On file size. The prose of Bluesky's posts guide says individual images are limited to 1,000,000 bytes, but the code sample on the same page rejects files above 2,000,000 bytes and says that limit comes from the lexicon. The current image embed schema and the newer gallery schema both say 2,000,000 bytes. Our recommendation: export under 1 MB and you are safe whichever number an app enforces.
The image count also changed recently. Bluesky's official account announced on June 8, 2026 that version 1.123 lets you attach up to 10 photos, with a redesigned carousel that only appears for posts with 5 or more. The gallery schema behind it sets a ceiling of 20 and tells apps to enforce a soft limit of 10 for now.
Do Threads and Bluesky crop feed images?
Neither publishes a crop rule for single images in the feed, so we cannot cite one. What they do document points the same way. Bluesky's posts guide says apps use the stored aspect ratio to display images without visual issues, which suggests the app knows each image's shape before it loads. Threads accepts ratios up to 10:1 and only rescales width, which suggests it is built to show tall and wide images rather than trim them to one shape.
Our recommendation is to stay between 4:5 and 1.91:1 anyway. Those shapes display comfortably in every feed we design for, including X's documented 2:1 to 3:4 range, and they leave you free to post the same file everywhere. Very tall infographics may be accepted by Threads but have no documented behavior on Bluesky, so test them before relying on them.
What should one shared file look like?
Build for the stricter platform, then post the same file to both. Below are two renders from our AURORA demo brand that pass every limit in the table.
The 4:5 portrait takes the most height in a phone feed that each platform documents as accepted. As a flat graphic exported as PNG, this file is far below 1 MB.
The square is the safest choice when the same image also goes to Instagram, LinkedIn and X. Our guide to repurposing one visual across platforms shows how to plan that from the start.
Our settings for a shared file (our recommendation):
- 1080 px wide, 4:5 or 1:1, sRGB color.
- PNG for flat graphics with text, JPG for photos; under 1 MB either way.
- Headline inside the central 80 percent of the canvas, so any app padding or preview crop leaves it whole.
- The same alt text pasted into both apps.
When do you need a different version?
In our experience, only in a few cases:
| Situation | Why one file fails | What to do |
|---|---|---|
| Photo-heavy JPG over 1 MB | Bluesky may reject it | Export a lighter copy for Bluesky |
| More than 10 images | Threads allows 20, Bluesky's app 10 | Split into two posts on Bluesky |
| Tall infographic, beyond 4:5 | Bluesky publishes no ratio behavior | Cut it into slides |
| Long explanation in the post text | Threads allows 500 characters, Bluesky 300 graphemes | Move detail into the image or a reply |
| Wider than 1440 px | Threads scales it down | Export at 1080 to 1440 px wide |
There is one more case that is about reach, not pixels. Instagram's Help Center explains that you can share Instagram posts to Threads once or automatically, but those cross-posted items are not sent to fediverse servers even if you share to the fediverse. Threads also warns that other servers may limit how media appears, including how many images are shown. If fediverse readers matter to you, post natively on Threads.
How do you keep both feeds on brand?
Use one template per ratio and the same fonts, colors and margins in each. In Chikaboom, a designer builds a layout once and the team fills in the text, which shrinks inside its box instead of overflowing, so a Threads post and a Bluesky post come from the same file. You can see the layouts in the live demo.
For the broader picture, our Instagram carousel design hub covers multi-image posts, the X header and post visual guide covers the network these apps are most often compared with, and the social media image sizes table lists every other platform.
Checklist before you post to both
- 1080 x 1350 or 1080 x 1080 px, sRGB, JPG or PNG.
- File under 1 MB, so Bluesky accepts it whichever limit applies.
- No more than 10 images if the post goes to Bluesky too.
- Post text under 300 characters, or a shorter version ready for Bluesky.
- Alt text written once and added in both apps; the Threads Help Center lists editing alt text among its post features.
- Posted natively on Threads if you want fediverse readers to see it.