September 24, 2026 · Reachira team · 6 min read

TikTok, Reels, Shorts: the format rules that get you shown

Length, aspect ratio, file specs, carousels and originality rules for TikTok, Instagram Reels and YouTube Shorts, taken from each platform's own docs.

Short-form platforms look alike from the outside: a vertical video, a caption, a feed. Underneath, each one has its own limits on length, shape and file, and its own idea of what content is worth recommending to people who do not follow you yet. A video can be accepted and still never be recommended, or land in the wrong place, like a Short that YouTube files as long-form.

This guide collects the rules that matter, platform by platform, and links every one of them to the platform's own documentation. Where a limit applies only to uploads made through a platform's API (which is how scheduling tools publish), we say so.

TikTok

Length

TikTok does not have one maximum length for everyone. Its Content Posting API media transfer guide says that all creators can post 3-minute videos, while some have access to 5- or 10-minute videos, and that the longest video a developer can send is 10 minutes. The same page warns that users may trim developer-sent videos in the app to fit their account's actual limit.

The real limit is per account. The creator info endpoint returns a max_video_post_duration_sec field and states that different users have different maximum video-duration privileges. If you publish through a tool, it should read that value rather than assume one.

File, frame rate and resolution

From the same media transfer guide:

Formats: MP4 (recommended), WebM, MOV.
Codecs: H.264 (recommended), H.265, VP8, VP9.
Frame rate: 23 to 60 FPS.
Picture size: at least 360 pixels and at most 4096 pixels on both height and width.
File size: up to 4 GB.

The guide sets pixel bounds rather than a required aspect ratio, so the shape is a creative choice.

Photo posts

TikTok photo posts are a separate media type. The photo post API reference accepts up to 35 images per post, and the media transfer guide limits each image to WebP or JPEG, a maximum of 1080p and 20 MB.

What keeps a video out of For You

TikTok's For You feed standards are explicit that not all content is guaranteed to be recommended, and that content matching the "FYF Ineligible" standards in its Community Guidelines will not be recommended in the For You feed. The same page notes that an ineligible video can still be found through search or on the creator's account, and that low views do not necessarily mean a rule was broken.

For content creators and brands, the most relevant ineligible categories sit in TikTok's Integrity and Authenticity guidelines:

Reused or unoriginal content posted without creative edits, such as clips that show someone else's watermark or logo.
Low-quality or minimally edited content, such as short clips made only from GIFs.

The same guidelines require a label on AI-generated or significantly edited content that shows realistic-looking people or scenes, and say unlabeled content may be removed, restricted or labeled by TikTok.

Instagram Reels

Length, shape and file

Instagram's content publishing API reference gives these Reel specifications:

Duration: 3 seconds minimum, 15 minutes maximum.
Aspect ratio: anywhere between 0.01:1 and 10:1, with 9:16 recommended to avoid cropping or blank space.
Frame rate: 23 to 60 FPS.
Picture size: at most 1920 horizontal pixels.
Container: MOV or MP4; video codec HEVC or H.264; audio AAC.
File size: up to 300 MB.

The same page says that if a Reel cover image is not 9:16, Instagram crops it to the middle 9:16 rectangle, and to a centred square when the Reel is shared to the feed. Keep important text and faces near the centre of the cover.

Length versus reach

Accepted is not the same as recommended. Instagram's creator FAQ says it recommends videos to unconnected audiences that are 3 minutes or less.

Carousels

A carousel is a separate post type. The same API reference says carousels can hold up to 10 images, videos or a mix, and that feed images must fall within a 4:5 to 1.91:1 aspect ratio. A 9:16 slide made for TikTok photo mode therefore does not fit an Instagram carousel image as-is.

Originality and watermarks

Instagram's recommendation guidelines list content that is allowed on the platform but may not be eligible for recommendation. One category is low-quality content, which includes unoriginal content that is largely repurposed from another source with only minor, immaterial edits and no added value. The guidelines also say Instagram tries not to recommend accounts that repeatedly and recently shared content prominently featuring a photorealistic AI-generated person, unless the account uses the AI-generated profile label.

The creator FAQ is direct about cross-posting: a third-party watermark on a Reel may be impacting its reach. Export a clean file for each platform instead of downloading your TikTok and re-uploading it.

YouTube Shorts

What counts as a Short

YouTube's three-minute Shorts page sets the rule: videos uploaded on or after 15 October 2024 with a square or vertical aspect ratio and up to three minutes long are categorised as Shorts. Videos uploaded before that date stay long-form. If you want a short video treated as long-form, YouTube's advice is to use a wider aspect ratio such as 16:9.

So a 40-second 16:9 clip is not a Short. The upload guide repeats the requirement: up to 3 minutes, square or vertical.

Copyright claims on longer Shorts

The three-minute Shorts page also says that, starting 24 September 2026, new Shorts longer than one minute (but under three) with an active Content ID claim will no longer be automatically blocked and may remain playable. If your Short uses third-party music or clips, a claim can still affect monetisation, and YouTube points you to removing the claimed content or filing a dispute.

Resolution

YouTube's recommended upload encoding settings list bitrates by resolution. At 1080p, the recommendation is 8 Mbps at standard frame rates (24, 25, 30) and 12 Mbps at high frame rates (48, 50, 60).

Originality and monetisation

YouTube's rules on originality mostly show up in monetisation. The channel monetization policies define "inauthentic content" as mass-produced or repetitive content. Examples that are not allowed to monetise include image slideshows, templated storylines or scrolling text with minimal narrative, and AI-generated content made from generic templates that gives the impression of mass production. "Reused content" is content taken from YouTube or elsewhere without significant original commentary, substantive changes, or educational or entertainment value.

The rules side by side

	TikTok	Instagram Reels	YouTube Shorts
Length	3 min for everyone; some accounts 5 or 10 min; per account	3 s to 15 min via API; recommended to non-followers at 3 min or less	Up to 3 min
Shape	Pixel bounds, no fixed ratio in API docs	0.01:1 to 10:1, 9:16 recommended	Square or vertical
Image posts	Photo mode, up to 35 images via API	Carousel, up to 10 items	Not covered here
Originality signal	Unoriginal, watermarked or minimally edited content is not eligible for For You	Repurposed content with immaterial edits may not be recommended; third-party watermarks may cut reach	Mass-produced and reused content cannot monetise

A practical checklist

Render per platform. One master edit, separate exports: no foreign watermarks, and covers framed for each platform's crop.
Check the account's TikTok limit rather than assuming 10 minutes.
Keep Shorts at three minutes or less and square or vertical, or YouTube will file them as long-form.
Keep Reels at three minutes or less if reaching non-followers is the goal.
Give each video its own substance. A new hook, a new angle and a new script count for more than swapping the background track.
Label realistic AI content where the platform requires it.

Reachira checks every video against each target platform's limits before publishing and skips any account where the video does not fit, without holding up the other platforms. For YouTube it applies a stricter cap of its own, 55 seconds. That is a product choice, not a YouTube rule, and it keeps videos well inside the Shorts limit. How often to post is a separate question, covered in what the daily posting cap means; which formats to post is covered on the formats page.

Sources

Practical notes on short-form video for software. No spam; unsubscribe any time.