Media requirements
File types, size limits and recommended dimensions for images and video you attach through the API.
Last checked against the API October 10, 2026 · View as Markdown
Accepted files
| Type | Formats | Maximum size |
|---|---|---|
| Image | JPEG, PNG, GIF, WebP | 10 MB |
| Video | MP4, MOV | 100 MB (raw upload), 10 MB (base64) |
- Upload every file with
POST /api/v1/mediaand attach the returnedurl. Links to files hosted elsewhere are rejected. - A post can carry up to 10 files.
- The file contents must match the declared type. SVG is not accepted.
- Images are stored as WebP. Platforms that need JPEG receive JPEG automatically.
- Larger videos can be uploaded in the Postprism app instead.
What each network does with media
| Platform | Uses | Needs media? |
|---|---|---|
| TikTok | One video, or a photo post of up to 35 images | Yes |
| YouTube | One video, plus an optional custom thumbnail | Yes, a video |
| One image | Yes, an image | |
| The first image or video | No | |
| X (Twitter) | Up to 4 images | No |
| Bluesky | Text only today; attachments are not posted | No |
Recommended dimensions
| Placement | Ratio | Pixels |
|---|---|---|
| Instagram feed (portrait) | 4:5 | 1080 × 1350 |
| Stories, Reels, TikTok | 9:16 | 1080 × 1920 |
| Square post (all feeds) | 1:1 | 1080 × 1080 |
| LinkedIn / Facebook link preview | 1.91:1 | 1200 × 627 |
| X in-feed image | 16:9 | 1600 × 900 |
| YouTube video and thumbnail | 16:9 | 1280 × 720 or larger |
| Pinterest pin | 2:3 | 1000 × 1500 |
More on sizing in the aspect ratio and safe zone guides, and free resizers in Tools.