Mastodon Post Size and Specs (2026)
Every Mastodon limit below comes from the rules PostQuest uses to check posts before they publish. Publishing limits were last verified on .
- Main post size
- Up to 16 MB (instance default)
- Photo Post
- Caption limit
- 500 characters (instance default)
- Instances configure their own limit; 500 characters is the default.
- Header
- 1500 × 500 px
Mastodon image and video specs
Text Post and Link Post use only the caption limit, so they have no media table.
Photo Post1 file
| Spec | Image |
|---|---|
| File size | Up to 16 MB (instance default) |
| Formats | JPEG, PNG, WebP (instance default) |
| Other limits | Up to 8.3 MP (instance default) |
Carousel Post2–4 files
| Spec | Image |
|---|---|
| File size | Up to 16 MB (instance default) |
| Formats | JPEG, PNG, WebP (instance default) |
| Other limits | Up to 8.3 MP (instance default) |
GIF Post1 file
| Spec | GIF |
|---|---|
| Dimensions | Up to 1,280 × 720 px (instance default) |
| File size | Up to 16 MB (instance default) |
| Formats | GIF (instance default) |
| Other limits | Up to 1 MP (instance default) |
Video Post1 file
| Spec | Video |
|---|---|
| File size | Up to 40 MB (instance default) |
| Formats | MP4, MOV, WebM (instance default) |
| Frame rate | Up to 120 fps (instance default) |
| Codecs | H.264 transcode |
Audio Post1 file
| Spec | Audio |
|---|---|
| File size | Up to 40 MB (instance default) |
| Formats | MP3, OGG, WAV, FLAC, Opus, AAC, M4A, 3GP (instance default) |
Mastodon caption and hashtag limits
Caption limit
500 characters (instance default)
Depends on the account or server.
- Instances configure their own limit; 500 characters is the default.
Hashtags
No hard limit
- No global hashtag-count limit.
- Bounded by the instance character limit, which defaults to 500 characters.
Accounts that can publish
Any local account that authorizes an OAuth application on the target instance.
Mastodon profile and banner sizes
| Image | Size | Details | Source |
|---|---|---|---|
| Header | 1500 × 500 px | Larger uploads are downscaled. WEBP, PNG, GIF, or JPG, up to 2 MB. | Mastodon docs: Setting up your profileVerified October 4, 2026 |
| Avatar | 400 × 400 px | Larger uploads are downscaled. WEBP, PNG, GIF, or JPG, up to 2 MB. | Mastodon docs: Setting up your profileVerified October 4, 2026 |
Mastodon specs FAQ
What size should a Mastodon post be?
A Mastodon photo post must meet these limits: file size up to 16 MB (instance default). No fixed pixel dimensions apply to this format.
What is the Mastodon character limit?
Mastodon captions can be up to 500 characters long by default. Instances configure their own limit; 500 characters is the default.
How many hashtags can you use on Mastodon?
Mastodon has no hard hashtag limit. Bounded by the instance character limit, which defaults to 500 characters.
What size is the Mastodon header?
1500 × 500 px. Larger uploads are downscaled. WEBP, PNG, GIF, or JPG, up to 2 MB.
Sources
Publishing limits last verified against official API documentation. Profile sizes last verified .
More platform specs
Schedule posts that pass these checks
PostQuest validates every caption and file against these limits before a post is scheduled, so nothing fails at publish time.