Instagram Guide: Formats, Limits and Best Practices

Aspect ratios, carousels, Reels length, hashtags and originality: what you need to know to post on Instagram, checked against official sources.

Published on September 27, 2026 · Social platforms

On Instagram, people size up a brand in a glance: the grid, the first frame of a carousel, the opening seconds of a Reel. And the platform has changed a lot in a short time. Carousels got longer in the app, the hashtag cap dropped, Reels can now run 20 minutes, and recycled content is treated more harshly than ever. This guide pulls together the formats and limits we verified against Instagram's and Meta's own documentation, what Instagram itself says about ranking, and a practical way to publish without leaving reach on the table.

Formats and specs

One distinction matters before anything else: what the Instagram app allows is not always what Meta's publishing API allows. Scheduling tools use the API, and the gap between the two is where most failed posts come from.

Feed photos

In the app, Instagram accepts images at least 1,080 pixels wide with an aspect ratio between 1.91:1 (landscape) and 3:4 (portrait), according to its Help Center. Through the API the range is narrower: 4:5 to 1.91:1, a maximum width of 1,440 pixels, 8 MB at most, and JPEG only, per Meta's developer documentation.

The safe default is 4:5 portrait at 1,080 × 1,350 pixels. It takes up more of the screen than a square and works everywhere, in the app and through the API.

Carousels

The app now lets you combine up to 20 photos and videos in a single post. The API still caps carousels at 10 items. Another API detail worth knowing: every image in a carousel is cropped based on the first one, with 1:1 as the default. Build every slide at the same ratio.

Reels

You can post Reels up to 20 minutes long, but Instagram's official Reels page states that Reels over 3 minutes won't be recommended to new audiences. The Creators FAQ says the same thing: recommendations to people who don't follow you target videos of 3 minutes or less. Through the API, a Reel must be between 3 seconds and 15 minutes. Full-screen vertical video is the standard.

Stories

Through the API, a Story video runs 3 to 60 seconds. Stories remain the format for the people who already follow you: behind the scenes, reminders, polls, and pointers to your latest posts.

Captions, hashtags and mentions

Captions can run up to 2,200 characters, but only the first lines show before "more." Your opening sentence has to carry the point, not a warm-up.

Hashtags changed significantly. On December 18, 2025, Instagram's official @creators account announced that Instagram now allows up to 5 hashtags per Reel or post. The API documentation still lists 30, but for a brand the practical rule is simple: a handful of specific hashtags that genuinely describe the topic beat a generic block of them. Hashtags help categorize content. They don't rescue a weak visual or a weak hook.

For partnerships, the collaborator feature shows a post on both profiles. Through the API you can invite up to 3 accounts, and their usernames must be sent without the "@". An "@handle" passed as-is gets rejected.

What the algorithm rewards right now

Instagram doesn't publish a formula, but it does describe its signals. In "Instagram Ranking Explained," the company says that for Reels it predicts how likely you are to reshare a Reel, watch it all the way through, like it, and visit its audio page. For Feed, it predicts how likely you are to spend a few seconds on a post, comment, like, share, or tap the profile photo.

The Creators FAQ sums up the most important factor as engagement per viewer: watch time, shares, follows, likes, comments and profile visits relative to the people who saw the content. Raw volume matters less than how the people who see a post react to it.

Originality now carries real weight

In April 2026, Instagram laid out its policy for rewarding original creators on its Creators blog. Accounts that mostly repost other people's work are no longer eligible for recommendations, and adding a border, a watermark, captions or a credit doesn't make content original. For a brand the takeaway is blunt: your own photos, your own video and your own ideas are the only solid foundation. A clip exported from another app with its watermark, or an image lifted from somewhere else, starts at a disadvantage.

Test without spamming followers: Trial Reels

Trial Reels, available to professional accounts, show a Reel to non-followers first. You can then share it with your followers manually or automatically based on how it performs. It's the right tool for testing a new hook or format without cluttering your followers' feeds.

How often to post

Instagram doesn't prescribe an ideal frequency, and no official source gives a universal number. The right cadence is the one you can sustain without the quality slipping. A realistic weekly base for a brand combines:

• short Reels to reach new people, since that's the format recommended to non-followers;
• carousels to go deeper on a topic, show a product range or walk through a method;
• Stories to keep the relationship going with existing followers.

Consistency beats volume. Three solid posts a week for six months will do more than a burst of ten followed by a month of silence. On the technical side, the API limits each account to 100 posts per rolling 24 hours, per Meta's content publishing docs, and a carousel counts as one post. No sensible editorial plan comes close, but the limit exists.

Common mistakes

1. Mixing ratios inside a carousel. Through the API everything gets cropped to the first image, so a landscape cover followed by portrait slides loses its subject.
2. Building a 12- or 15-slide carousel for a scheduling tool. The app takes 20, the API takes 10. Anything beyond that fails.
3. Using Reels over 3 minutes to grow. They aren't recommended to non-followers. Keep long formats for your existing audience.
4. Pasting 30 hashtags. The cap is now 5. Pick the most specific ones.
5. Recycling watermarked content. Originality is explicitly rewarded, and content imported untouched from another platform is penalized.
6. Typing a collaborator as "@handle" in a publishing tool. The API expects the bare username.
7. Putting key text at the edges of the image. Grid and preview crops cut it off. Keep headlines and logos in the central area.
8. Skipping alt text. It makes your images accessible to people with low vision and describes what they show.

Pre-publish checklist

• Feed visual at 4:5 (1,080 × 1,350 px), JPEG if you publish through a tool.
• Carousel: 10 slides max through a tool, all at the same ratio, with the first slide designed as a cover.
• Vertical Reel, hook in the first seconds, 3 minutes max if the goal is discovery.
• A first caption line that gives people a reason to keep reading.
• 5 hashtags or fewer, all relevant.
• Collaborators entered without "@", 3 max through the API.
• Alt text written for every image.
• Original content: no watermark from another app, no borrowed visuals.
• A Story to point your followers to the new post.

Keeping up without doing it all by hand

The hard part of Instagram isn't knowing these rules. It's applying them to every single post, alongside the rules of every other network you're on. With Oposto, you describe your brand once: it learns your voice, colors, products and audience from your website, prepares posts, image carousels, design carousels and short videos in the right format for Instagram, plans them in a calendar and publishes them at the scheduled time. Then it measures real performance and reuses what works.

Want to see next month's Instagram content ready for your review? Try Oposto: describe your brand once, it prepares a month of content in the right format for each network, and you approve.