Image Specs
Post Image
| Dimensions | Uploads up to ~33.2 MP accepted; stored downscaled to ~8.3 MP (3840 × 2160 px) |
|---|---|
| Max File Size | 16 MB (mastodon.social default; varies by instance) |
| File Formats | JPG, PNG, GIF, WEBP |
| Notes | Up to 4 images per post; each instance may set different limits; HEIF/HEIC and AVIF are temporarily disabled on mastodon.social for security reasons |
Profile Photo
| Dimensions | 400 × 400 px (downscaled from upload) |
|---|---|
| Max File Size | 8 MB (Mastodon 4.6+; older instances 2 MB) |
| File Formats | JPG, PNG, GIF, WEBP |
| Notes | Animated GIFs supported for avatar; displayed as a circle |
Profile Header Banner
| Dimensions | 1500 × 500 px (downscaled from upload) |
|---|---|
| Aspect Ratio | 3:1 |
| Max File Size | 8 MB (Mastodon 4.6+; older instances 2 MB) |
| File Formats | JPG, PNG, GIF, WEBP |
[Ad]
Video Specs
Post Video
| Max File Size | 99 MB (mastodon.social default; varies by instance) |
|---|---|
| File Formats | MP4, MOV, WEBM, M4V |
| Resolution | Up to 3840 × 2160 px (~8.3 MP) on mastodon.social |
| Notes | H.264 + AAC recommended; instance admins set upload limits |
Animated GIF
| Max File Size | 16 MB |
|---|---|
| File Formats | GIF |
| Notes | Converted to a soundless MP4 on upload; dimensions downscaled to stay under ~1 megapixel (e.g. 1280 × 720) |
Text & Character Limits
Post (Toot)
| Character Limit | 500 characters |
|---|---|
| Notes | Default on mastodon.social; instance admins can increase this limit |
Content Warning / Subject
| Character Limit | 500 characters |
|---|---|
| Notes | Optional CW hides post body until clicked; CW text and post body share the same 500-character budget |
Display Name
| Character Limit | 40 characters |
|---|---|
| Notes | Confirmed against mastodon.social's live /api/v2/instance config (max_display_name_length: 40); raised from an older 30-character figure |
Bio
| Character Limit | 500 characters |
|---|---|
| Notes | Supports HTML-style formatting; links in bio are auto-verified |
Profile Metadata Fields
| Character Limit | 4 fields |
|---|---|
| Notes | Each field label up to 255 characters, value up to 255 characters |
Profile Assets
Profile Photo
| Dimensions | 400 × 400 px (downscaled from upload) |
|---|---|
| Max File Size | 8 MB (Mastodon 4.6+; older instances 2 MB) |
| File Formats | JPG, PNG, GIF, WEBP |
| Notes | Displayed as a circle |
Header Banner
| Dimensions | 1500 × 500 px |
|---|---|
| Aspect Ratio | 3:1 |
| Max File Size | 8 MB (Mastodon 4.6+; older instances 2 MB) |
| File Formats | JPG, PNG, GIF, WEBP |
Visibility & Discovery
Hashtag
| Character Limit | No set limit characters |
|---|---|
| Notes | Hashtags are the primary discovery mechanism; no ads on the federated network |
Poll Options
| Character Limit | 4 options |
|---|---|
| Notes | Each option up to 50 characters on mastodon.social (per its live /api/v2/instance config; the generic Mastodon software default is 25 and varies by instance); polls can run 5 minutes to ~30 days on mastodon.social |