Mastodon Sizes & Dimensions Guide
Complete specifications for all Mastodon content types. Get the exact dimensions, aspect ratios, and file requirements for Mastodon. Updated for 2026.
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Mastodon Content Specifications
Image Post
Updated 2026Up to 4 images per post. Large images are downscaled; size limits vary by server.
Dimensions
1280×720+ recommended
Aspect Ratio
16:9, 1:1, or original
Max Size
~16 MB default (varies by server)
Format
JPG, PNG, GIF, WEBP, HEIC
Images per PostUp to 4
DownscalingImages over ~8 MP are resized
Alt TextSupported (recommended)
Video / GIF
Updated 2026In-feed video. Maximum size and length depend on the server you post from.
Dimensions
1280×720 (or 1920×1080)
Aspect Ratio
16:9 or 1:1
Max Size
~40–99 MB default (varies by server)
Format
MP4, WebM, MOV
Duration
Varies by server (often ~60 sec)
Avatar
Updated 2026Profile picture, displayed as a rounded square.
Dimensions
400×400
Aspect Ratio
1:1
Max Size
~2 MB default
Format
JPG, PNG, GIF
Header
Updated 2026Profile banner shown at the top of your Mastodon profile.
Dimensions
1500×500
Aspect Ratio
3:1
Max Size
~2 MB default
Format
JPG, PNG, GIF
Mastodon Content Best Practices
Limits vary by instance — check your server's about page for exact media caps
Always add alt text; Mastodon's culture strongly expects described images
Keep images under ~8 MP to avoid automatic downscaling and quality loss
Use a 3:1 header (1500×500) so it isn't cropped on the profile banner
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