One file comes close to fitting all six: an MP4 with H.264 video and AAC sound, 1080 by 1920, 24 frames a second, 3 to 90 seconds long and under 300 MB. X is the open question, because its docs list 1280 by 1024 as the largest size. These numbers come from each platform’s developer docs, which cover posting through an app. Uploading by hand in the app can differ.
What each platform accepts
| Platform | Length | File size | Frames a second | Shape |
|---|---|---|---|---|
| TikTok | Up to 10 minutes, or your account’s limit | 4 GB | 23 to 60 | Each side 360 to 4096. No ratio rule stated |
| Instagram Reels | 3 seconds to 15 minutes | 300 MB | 23 to 60 | Up to 1920 wide. 9:16 suggested |
| YouTube | 15 minutes unless verified. Shorts up to 3 minutes | 256 GB | Not stated | Shorts are square or vertical |
| Facebook Reels | 3 to 90 seconds | Not stated | 24 to 60 | 9:16, at least 540 by 960 |
| X | 0.5 seconds to 20 minutes | 8 GB | Up to 60 | 1:3 to 3:1. Largest listed is 1280 by 1024 |
| 3 seconds to 30 minutes | 75 KB to 500 MB | Under 30, ads page only | 16:9, 1:1, 4:5, 9:16, ads page only |
Why that one file
- 3 to 90 seconds: Instagram, Facebook and LinkedIn all start at 3 seconds, and Facebook Reels stop at 90.
- Under 300 MB: that’s Instagram’s limit, the lowest stated.
- 24 frames a second: TikTok and Instagram start at 23, Facebook at 24, and LinkedIn’s ads page says under 30.
- 1080 by 1920: vertical fits TikTok, Reels, Shorts and LinkedIn. We haven’t posted one to X yet, so we can’t say what its size limit does in practice.
Words and tags
| Platform | Caption | Hashtags |
|---|---|---|
| TikTok | 2,200 | No limit stated |
| 2,200 | 5. Trade press says it was cut from 30 in December 2025, while Meta’s API page still says 30 | |
| YouTube | Title 100 characters. Description 5,000 bytes | Over 60 and all are ignored |
| Not stated | Not stated | |
| X | 280, and a link counts as 23 | Count as normal text |
| 3,000, from a help page | Not stated |
Rules most size charts leave out
- TikTok tells apps not to add any brand name, logo, watermark, link or promotional text to content shared through them. If you post by hand, that rule isn’t aimed at you. If an app posts for you, ask it what it adds.
- TikTok says realistic AI content must be labeled, and YouTube requires a label for realistic altered or made-up content.
- TikTok asks for about 15 posts a day at most per account when posting through an app, and Facebook allows 30 Reels in 24 hours.
- Instagram’s head said in October 2024 that it tries not to recommend Reels with logos from other apps, though your own logo is fine. So give Reels a clean file, not one saved from TikTok with its watermark.
- New York has a rule on AI-made people in ads. We’ve only read a law firm’s summary, so ask a lawyer if yours appear in one.
We wrote this because Lou by Luven AI, the video tool we’re building, has to follow these rules. Lou isn’t open yet, and nothing here has been tested on a real account. Platforms change their docs, so check before a big launch. We’ll date every update. To check a file against all six, try our free checker.
Sources, read 3 Nov 2026
- TikTok media transfer guide
- TikTok content sharing guidelines
- Instagram media reference
- Social Media Today on Instagram hashtags
- YouTube upload reference
- YouTube Shorts help
- YouTube altered content help
- Facebook Reels publishing
- X media best practices
- LinkedIn videos API
- LinkedIn video ads specs
- TikTok community guidelines
- Social Media Today on Instagram and logos
- Hunton on New York’s rule
How we write these: with AI help, from the sources we link, with dates. Counts marked as ours were made by an AI reader with no second check. If something’s wrong, email everest@luven.ai and we’ll fix it and say so.
