Key takeaways
- Instagram accepts JPEG images only through SkedCast’s adapter — PNG and WebP are converted to JPEG before publishing.
- YouTube accepts no image posts at all — every upload is a video, up to 43,200 seconds (12 hours) long.
- Aspect ratio rules vary from a tight 4:5–1.91:1 range on Instagram to Bluesky, which recommends but does not enforce a ratio.
- File size ceilings range from 1MB for a Bluesky image up to 10,240MB (10GB) for a Facebook video.
Social media image sizes 2026: specs at a glance
Format, aspect ratio range, and file size ceiling for images, and duration plus file size for video, per platform. These are the ADAPTER-enforced ceilings SkedCast publishes within today, which are sometimes tighter than what a platform’s API technically allows.
- X (Twitter) image: jpeg/png/webp/gif, up to 4 per post, 5MB max, aspect 3:4–2:1
- X (Twitter) video: mp4/quicktime, 512MB max, up to 140s
- LinkedIn image: jpeg/png/gif, up to 20 per post, 5MB max, aspect 4:5–1.91:1
- LinkedIn video: mp4/quicktime/webm, 5,120MB max, up to 1800s
- Instagram image: jpeg, up to 10 per post, 8MB max, aspect 4:5–1.91:1
- Instagram video: mp4/quicktime, 1,024MB max, up to 900s
- Facebook Pages image: jpeg/png, up to 10 per post, 10MB max, aspect 9:16–16:9
- Facebook Pages video: mp4/quicktime, 10,240MB max, up to 14400s
- TikTok image: jpeg/webp/png, up to 35 per post, no adapter file-size cap, aspect 9:16
- TikTok video: mp4/quicktime/webm, 4,096MB max, up to 600s
- YouTube video: mp4/quicktime/webm/x-msvideo, 262,144MB max, up to 43200s
- Threads image: jpeg/png, up to 20 per post, 8MB max, aspect 1:10–10:1
- Threads video: mp4/quicktime, 1,024MB max, up to 300s
- Pinterest image: jpeg/png, up to 5 per post, 20MB max, aspect 2:3
- Pinterest video: mp4/quicktime/x-m4v, 2,048MB max, up to 900s
- Bluesky image: jpeg/png/webp, up to 4 per post, 1MB max, aspect 1:1, 4:5, 16:9, 1.91:1
- Bluesky video: mp4/mpeg/webm/quicktime, 300MB max, up to 180s
- Telegram image: jpeg/png, up to 10 per post, 10MB max, aspect flexible
- Telegram video: mp4, 50MB max, up to 300s
Why the adapter ceiling, not just the platform’s own limit
A platform’s official API sometimes allows more than SkedCast’s adapter publishes today — for example TikTok’s photo carousel technically allows more images than earlier adapter versions supported. The numbers above are what actually publishes through SkedCast right now, so a file that passes this check will not fail at publish time for a reason this guide didn’t warn about.
For exact recommended pixel dimensions (not just aspect ratio) on a specific platform, use that platform’s dedicated image size guide — this article intentionally does not re-type those pixel numbers, so the two pages can never quietly disagree.
FAQ
- What image format does Instagram actually accept?
- JPEG only through SkedCast’s adapter — a PNG or WebP file is converted to JPEG automatically before it publishes.
- Can I post an image to YouTube?
- No — YouTube accepts video uploads only; there is no image-post format on the platform’s publishing API.
- What is the maximum video length for YouTube?
- Up to 43,200 seconds (12 hours) per video through SkedCast’s adapter, with no enforced minimum duration.
- Which platform has the smallest file size limit for images?
- Bluesky has the tightest image file-size ceiling among the platforms covered here, at 1MB per image.
- Do these specs cover exact pixel dimensions?
- No — this guide covers aspect ratio range, format, file size and duration; each platform’s dedicated image-size tool page gives the exact recommended pixel dimensions.
- Why do some platforms show a strict aspect ratio range and others only a recommendation?
- A platform like Instagram enforces a hard 4:5 to 1.91:1 range and rejects anything outside it, while a platform like Bluesky only recommends a ratio without enforcing one — this guide states which applies per platform.
- Where do these numbers come from?
- From SkedCast’s own composer registry — the exact adapter-enforced rules the product uses when validating an upload, not independently estimated figures.