Mastodon Image Size

The recommended image dimensions for Mastodon profiles, headers, and posts in 2026

Mastodon is the largest decentralized social network, with millions of users spread across thousands of independently-run servers. Unlike centralized platforms, each Mastodon instance can set its own upload limits - but the display sizes stay consistent across the network. If you've used Twitter/X or Bluesky, the interface will feel familiar: short text posts, image attachments, and a timeline feed. Here's everything you need to know about Mastodon image sizes so your posts and profile look clean on any instance.

Mastodon Profile Picture Size

Your Mastodon avatar should be 400 x 400 pixels with a 1:1 aspect ratio. The platform displays profile pictures as rounded squares (with soft corners) throughout the interface - in your profile, in timelines, in notifications, and in reply threads. Some instances or third-party apps display them as circles instead, so keeping your subject centered is a good idea regardless.

Mastodon accepts PNG, JPG, and GIF formats for profile pictures. Yes, animated GIFs work as avatars on Mastodon - something most other platforms dropped years ago. The default file size limit is 2 MB, though some instances set this higher or lower. If your image exceeds the limit, your instance will reject the upload with an error message.

Your avatar appears at different scales depending on context. It's about 46 pixels across in the timeline and much larger on your profile page. Simple, high-contrast images with bold shapes work best at small sizes. Detailed photos or logos with fine text tend to become unreadable when they shrink down in the feed.

Mastodon Header Image Size

The Mastodon profile header image should be 1500 x 500 pixels with a 3:1 aspect ratio. This wide banner sits at the top of your profile page, behind your avatar and bio information. It's the first thing visitors see when they check out your account, so it's worth making it look good.

On mobile, the header gets cropped tighter on the sides and your avatar overlaps the bottom-left portion. Keep important visual elements centered and away from the edges. Gradients, patterns, and wide landscape photos tend to work better than text-heavy designs. The default file size limit is 2 MB.

Unlike some platforms, Mastodon doesn't compress your header aggressively. If you upload a crisp 1500 x 500 PNG, it stays sharp. But PNG files can be large, so if you're close to the file size limit, switching to JPG at 85-90% quality usually looks identical and saves a lot of space.

Mastodon Post Image Size

Mastodon post images can be up to 4096 x 4096 pixels on the default Mastodon software, though most instances set a practical limit around 1920 x 1080 pixels or similar. For the best display in timelines, a 16:9 landscape format at 1920 x 1080 pixels fills the feed width nicely. Square images at 1080 x 1080 pixels and portrait images at 1080 x 1350 pixels also display well.

You can attach up to 4 images per post (or 1 video/GIF). Multiple images appear in a grid layout that adapts based on how many you include and their aspect ratios. Mastodon generates preview thumbnails for the timeline and lets users click to view the full-resolution version. The default file size limit per image is 16 MB for standard images, which is generous compared to most platforms.

One important Mastodon feature: every image gets a "focal point" selector when you upload it. This tells the platform which part of the image to keep visible when generating cropped thumbnails. Set the focal point on the most important part of your image (a face, the main subject) and the timeline preview will always center on that spot, even if the aspect ratio doesn't match the display area.

Mastodon strongly encourages adding alt text to images for accessibility. Many instances show a visual indicator when an image has alt text, and some users filter their feeds to only boost posts that include descriptions. Taking a minute to describe your images isn't just good practice - it actually helps your posts reach more people on the platform.

Mastodon Video Dimensions

Mastodon supports video uploads with a default maximum file size of 99 MB and a duration limit that varies by instance (commonly 5 minutes on larger servers, sometimes longer on smaller ones). The platform accepts MP4 and WebM formats. For the best playback quality, upload in 16:9 landscape at 1920 x 1080 pixels or 9:16 portrait at 1080 x 1920 pixels.

Videos play inline in the timeline with click-to-play controls. They don't autoplay by default, which is a deliberate design choice by Mastodon. If you're cross-posting video content from TikTok or YouTube Shorts, the 9:16 portrait format works natively on Mastodon as well. Mastodon also supports audio-only uploads for podcasters and musicians.

Mastodon Custom Emoji Size

Mastodon instances can create custom emoji, and each one should be 128 x 128 pixels or smaller, with a maximum file size of 256 KB. Custom emoji are displayed inline with text at roughly 20-24 pixels, so simpler designs read better than detailed ones. Animated GIF and APNG emoji are supported on most instances.

If you run your own instance or have admin access, custom emoji are uploaded through the admin panel. Users on any instance can use them with the shortcode syntax (:emoji_name:). Many instances share popular emoji packs, and there's a community culture around creating and distributing custom emoji sets. Transparent PNG backgrounds work best so the emoji blends naturally with any theme.

Mastodon Link Preview (OpenGraph) Size

When you share a link on Mastodon, the platform fetches the OpenGraph image from the page and displays it as a link preview card below your post text. The ideal size for link preview images is 1200 x 630 pixels with a 1.91:1 aspect ratio. This is the same standard used by Facebook, LinkedIn, and most other platforms for link cards.

Mastodon caches link previews when they're first fetched, so if you update your page's OG image after someone has already shared the link, you may need to wait for the cache to expire (or ask your instance admin to clear it). For your own posts, you can edit the post to re-fetch the preview.

Instance Differences and Upload Limits

Because Mastodon is decentralized, different instances can have different upload limits. The defaults in the standard Mastodon software are generous - 16 MB for images, 99 MB for video, 2 MB for avatars. But instance admins can adjust these up or down based on their server capacity and storage costs. Some large instances like mastodon.social stick close to defaults, while smaller hobby instances might have tighter limits.

Forks of Mastodon like Glitch-soc and compatible software like Pleroma and Akkoma may also have different limits. Glitch-soc, for example, supports up to 16 attachments per post instead of the standard 4. If you're on a non-standard instance, check your instance's about page or ask the admin for specific limits. The image display sizes and aspect ratios stay the same across the entire Fediverse, though - it's just the upload limits that vary.