Bluesky is newer than the rest of the platforms I make assets for, so the size guides for it are all over the place. One says the avatar is 400 square, the next says 1000, a third tells you the banner is 1500x500 and then the one below it says 3000x1000. They're sort of all right, which is the annoying part. And a lot of them are stale on the file limits, which Bluesky just changed. So I built the version I actually trust: the current sizes, the safe zones, and the one limit that will still quietly wreck your image if you ignore it. It's the Bluesky slice of the full social media image size guide, which does the same thing for every other platform.
The file limits are the part most guides get wrong now. Back on April 7, 2026 Bluesky raised the cap on a posted image from about 1MB to 2MB and bumped the largest stored dimension from 2000px to 4000px (it's in atproto discussion 4832 if you want to read the thread). So for normal posts you've got way more room than the old guides say. The catch is that the avatar and the banner run on a separate upload path, and that one still caps around 1MB. So your photos are fine, but a 3000x1000 banner with text or a logo still has to be squeezed under ~1MB by hand, and if you don't do it the app compresses it for you and usually picks the spot where your text goes fuzzy. That avatar and banner ceiling is the real thing left to watch on Bluesky.
Here's the whole set. Pick a surface, copy the size, or grab the template.
The two on your profile
The avatar is 1000 x 1000 and Bluesky masks it to a circle, the same way most apps do now. So the corners are gone, and anything you tuck into a corner goes with them. Keep your face or your mark centered with a little room around it. You'll see 400x400 listed in a lot of guides and that still renders fine, it's just the floor. I upload at 1000 because it stays sharp when Bluesky shows your avatar tiny in a reply thread and also when someone opens it full size.
The banner is 3000 x 1000, a wide 3:1 strip behind your name. This is the one people get wrong, because your avatar overlaps the lower-left corner of it and mobile crops the sides in a little tighter than desktop. So if you put your logo or your handle down in the bottom-left, your own profile photo sits on top of it. Keep the important art centered and pulled up off the bottom edge. A 1500x500 banner works too at the same ratio, but at 3000 wide it holds up on a big monitor without going soft.
Feed posts: square is the safe pick
Most of Bluesky is the feed on a phone, so I default to a square 1000 x 1000. It fills the mobile feed width and never gets letterboxed into a weird shape. You can post up to 4 images per post, and the 2MB cap is per image, so there's plenty of headroom now even with four photos in one post.
A landscape 1200 x 675 (16:9) works when the shot is wide, and a portrait 1200 x 1500 (4:5) eats the most vertical space as someone scrolls past, which is usually what you want on mobile. One thing to know: since April 2026 Bluesky stores the long edge of a posted image up to 4000px, double the old 2000px limit, so your source has room to stay sharp. You still don't need to send something enormous, since anything past 4000px gets resized and a fatter file just compresses harder to fit under 2MB.
When you share a link, Bluesky pulls a card image at 1200 x 630 from the page's og:image tag. If you own the page, set that tag and you decide what the card shows. If you don't, Bluesky grabs whatever it can find, which is usually the wrong thing.
Alt text is basically expected here
This part is more culture than spec, but it matters on Bluesky specifically. The community there cares a lot about image accessibility, and posting an image with no alt text gets noticed in a way it doesn't on most platforms. The good news is the alt text field is generous, you get up to around 1,000 characters, and it doesn't count against your post's character limit. So describe what's in the image properly. It's free, it helps people who use screen readers, and on Bluesky it's just the expected thing to do.
File sizes and formats, quick version
The file caps split by surface now. Posts get a 2MB per-image cap since April 2026, which is roomy, so a JPG at 80-85% quality clears it easily and still looks clean. The avatar and banner are the tight ones, still around 1MB on their own upload path. For the banner, drop to about 70-80% quality because you're spreading that smaller budget across a much wider canvas. PNG is fine for a mark or a flat graphic with hard edges, but a photographic PNG will balloon fast, so reach for JPG on anything with gradients or a lot of detail. WebP is the quiet winner for posts when your tool exports it well, it gets you the most quality per kilobyte. Avatars and banners stick to PNG or JPG.
“Posts get 2MB now, but the avatar and banner still cap around 1MB. Squeeze the banner under that yourself, or the app compresses it for you and picks where it goes soft.
”
Just grab the template
If you don't want to do the math, hit the template pack button up in the tool. You get a correctly sized canvas for every Bluesky surface, named so you know which is which, with the safe area and the avatar crop drawn right on it. Drop the banner one into Figma or Photoshop as a reference layer, design on top of it, then export to JPG and watch the file weight. The pixel dimensions are already handled, so the only thing left for you to solve is getting that banner under ~1MB.
It's the same idea I use for the print dimensions tool, pointed at screens instead of paper. If you build assets for both, the print one handles DPI and bleed the way this one handles crops and the file caps.
If you cross-post, I built matching pages for the two networks closest to Bluesky in feel: Threads image sizes and Twitter/X image sizes. Same copy-paste numbers and template packs, just sized for where each one crops.
FAQ
What is the Bluesky banner size in 2026?
The Bluesky banner is 3000 x 1000 pixels, a 3:1 ratio. A 1500 x 500 banner works at the same ratio if you want a smaller file. Posts got a bigger 2MB cap in April 2026, but the banner did not, so keep it under the ~1MB it still allows. Your avatar also covers the lower-left corner, so keep key art centered and up off the bottom edge.
What size should a Bluesky avatar be?
1000 x 1000 pixels, square. Bluesky masks it to a circle, so center your face or mark and leave room around it. 400 x 400 is the floor that still renders, but 1000 stays sharp when the avatar shows up tiny in a thread or full size when tapped.
Why does Bluesky make my image blurry?
Usually it's the banner. Posts got a 2MB cap in April 2026, but the avatar and banner still run on a separate path that caps around 1MB, so a detailed banner gets compressed down to fit and that's where text and fine detail go soft. Export the banner as JPG at 70-80% quality so it lands under ~1MB before the app does its own pass.
What is the best Bluesky post image size?
A 1000 x 1000 square is the safe all-rounder for the mobile feed. Use 1200 x 675 for a wide shot or 1200 x 1500 for portrait, which takes the most vertical room. Since April 2026 Bluesky stores the long edge up to 4000px and caps a posted image at 2MB, so you've got real headroom, though anything past 4000px still gets resized.
How many images can you post on Bluesky and do they need alt text?
Up to 4 images per post, and the 2MB cap is per image, so you've got room for all four. Alt text isn't required by the app, but the Bluesky community strongly expects it. You get up to ~1,000 characters and it doesn't count against your post length, so there's no reason to skip it.
The full set, with the safe zones and the templates, is in the tool at the top. Copy what you need, or take the whole pack.