Key takeaways
- One 9:16 file can serve all three: YouTube treats a square or vertical video of up to three minutes as a Short.
- Export from your editor, not from another app: Instagram has said it tries not to recommend Reels carrying logos from other apps.
- Fields that differ: TikTok requires a privacy level, YouTube requires a title (up to 100 characters), Instagram requires a Professional account.
- Publish times: Buffer’s 2026 data has Reels evening-heavy midweek, Shorts peaking Friday evening, and TikTok in conflict with Sprout Social’s — so stagger rather than post all three in the same minute.
What do you need to post Reels, Shorts and TikTok at once?
These are the limits SkedCast’s composer enforces for video on each platform, read from the same rulebook the publishing adapters use. They are upload ceilings, not recommendations: the platforms’ own tools favour much shorter clips.
| Spec | YouTube | TikTok | |
|---|---|---|---|
| Video length (SkedCast ceiling) | 3 s – 15 min | up to 720 min (a Short is 3 min or less) | 3 s – 10 min |
| File size | 1,024 MB | 262,144 MB | 4,096 MB |
| Recommended aspect | 9:16 | 16:9, 9:16 | 9:16, 1:1, 16:9 |
| Formats | mp4, quicktime | mp4, quicktime, webm, x-msvideo | mp4, quicktime, webm |
| Caption or description | 2,200 characters | 5,000 characters | 2,200 characters |
| Hashtag cap | 30 | 15 | none |
| Required extras | Professional account | A title (from the caption’s first line) | A “who can view” privacy level |
| First comment | Yes | Yes | No |
How do you make one file that works on all three?
Make a 9:16 video at 1080×1920. YouTube’s help centre says any video uploaded on or after 15 October 2024 that is square or vertical and up to three minutes long is categorised as a Short, so a vertical file under three minutes is a Short without any extra field. Keep the important content inside the centre of the frame so each app’s buttons and captions do not cover it, and put any burned-in captions where all three leave room.
Export from your editor, not from another app. Instagram has said it tries not to recommend Reels that carry logos from other apps, while a logo of your own is fine — so a file saved out of another app with its watermark can cost you discovery on Reels. The clean master is the one to schedule everywhere.
How do you publish it to all three at once?
In SkedCast:
- Upload the finished file to the media library once.
- In the composer, tick the Instagram, YouTube and TikTok accounts and attach the video.
- Write the base caption, then adjust per platform: TikTok and Instagram captions can be short; the YouTube version’s first line becomes the title (up to 100 characters) and the rest the description.
- Set the TikTok “who can view” option — it is required and never guessed — and add an Instagram cover if you want one.
- Choose the times. Publishing all three in the same minute is possible, but the best windows differ, so staggering them usually makes more sense.
When should each one go out?
Buffer’s 2026 analyses point in different directions for each. Reels follow a midweek evening pattern (6–11 p.m.); YouTube Shorts peak on Friday at 4, 6 and 7 p.m.; TikTok has Buffer favouring Sunday morning and evenings while Sprout Social favours Tuesday to Friday, 2–6 p.m. — a direct conflict. The Instagram, YouTube and TikTok posting-schedule guides show each study and how to test your own account.
Does posting the same video everywhere hurt performance?
We did not find a reliable study measuring that, so this guide does not claim an effect either way. What is documented is narrower: Instagram tries not to recommend Reels carrying other apps’ logos, and each platform judges a video on its own audience response. The practical answer is to use the clean master, write a caption native to each platform, and measure each platform on its own numbers.
Sources
FAQ
- Can I post one video to TikTok, Reels and YouTube Shorts at the same time?
- Yes, from a scheduler that publishes to all three: upload one vertical file, tick the three accounts, and set a caption per platform. TikTok needs a “who can view” setting and YouTube a title.
- How long can a YouTube Short be?
- Up to three minutes: YouTube’s help centre says a square or vertical video up to three minutes long, uploaded on or after 15 October 2024, is categorised as a Short.
- Should I download my TikTok and upload it to Reels?
- Use the clean file from your editor rather than a download carrying another app’s logo: Instagram has said it tries not to recommend Reels with logos from other apps.
- What is the best aspect ratio for all three?
- Vertical 9:16, at 1080×1920. It is the recommended shape for Instagram Reels and TikTok and qualifies as a YouTube Short.
- Do I need separate captions for each platform?
- Not strictly, but the fields differ: YouTube’s first caption line becomes the title (up to 100 characters), Instagram has a 30-hashtag cap, and TikTok has none. A short native caption per platform reads better than one shared block.