SocialRobot· Updated 2026
Mastodon image & video sizes (Updated 2026)
Mastodon limits are instance-configurable. SocialRobot uses common defaults (16 MB images, ~8.3 MP matrix, 40 MB video) so posts succeed on typical servers.
All Mastodon sizes at a glance
Updated 2026
| Content type | Dimensions | Aspect ratio | Max file size | Formats |
|---|---|---|---|---|
| Post image | Long edge up to 3840; matrix ≤8.3 MP | Flexible | 16 MB (default) | JPEG, PNG, GIF, WebP |
| Video | Long edge up to 1920 | Flexible | 40 MB (default) | MP4, WebM, MOV |
Mastodon content specifications
Post image
- Dimensions
- Long edge up to 3840; matrix ≤8.3 MP
- Aspect ratio
- Flexible
- Max size
- 16 MB (default)
- Formats
- JPEG, PNG, GIF, WebP
- Length / count
- Up to 4 attachments
Video
- Dimensions
- Long edge up to 1920
- Aspect ratio
- Flexible
- Max size
- 40 MB (default)
- Formats
- MP4, WebM, MOV
- Length / count
- Up to 300 seconds (5 min)
Best practices
- Stay under 16 MB and ~8.3 megapixels for images.
- Prefer JPEG or WebP for photos.
- Keep video under 40 MB and five minutes when using defaults.
Common mistakes
- Uploading huge phone photos that exceed the matrix limit.
- Assuming every instance uses the same caps.
- Attaching more than four media items.
Sizes for other platforms
Publish to Mastodon at the right size
SocialRobot crops and compresses at publish. Upload once, tweak the crop if you want, and schedule across your channels.
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