Bluesky is more generous with source image size than most platforms, and its banner is unusually wide at a 3:1 ratio. That combination catches people out in both directions: a banner cropped for another network looks wrong here, and an image exported small to save space ends up softer than it needed to be.
Here are the dimensions Bluesky actually uses.
| Type | Size | Aspect ratio |
|---|---|---|
| Profile Photo | 400 x 400 | 1:1 |
| Banner | 3000 x 1000 | 3:1 |
| Post Image | 2000 x 2000 | 1:1 |
| Post Image (Landscape) | 2000 x 1125 | 16:9 |
Which size to actually use
2000 x 2000 is the working size for a standard post image, and 2000 x 1125 is the one to use when the photo is naturally wide. Both are larger than the equivalent sizes on most networks, which works in your favor: Bluesky displays a scaled-down version in the timeline and keeps the larger file for anyone who taps to expand it.
Bluesky allows up to four images in a single post. Keeping all four at the same ratio makes the grid it builds look intentional rather than mismatched, the same way it does on any platform that tiles multiple images.
The banner is the one to get right by building at the actual size. At 3000 x 1000 it’s much wider than a typical header, so an image designed for a 1500 x 500 header elsewhere will look stretched or heavily cropped if you reuse it without adjusting.
Format and common mistakes
Export as JPEG for photos and PNG when you need transparency or sharp text over a background. Uploading a phone photo shot in portrait and letting Bluesky crop it is the most common misstep here, a social media image resizer fixes the ratio before you post instead of after.
If you want to check how an image will actually display, a Bluesky image size checker confirms it before you commit. And if you’re formatting for more than one platform at once, the social media image size guide keeps the numbers straight without ten browser tabs open.
Because the recommended sizes here are larger than most, file size adds up faster than you’d expect on a four-image post. An image compressor brings each one down without a visible drop in quality.