TLDR
In the Threads app, tap +, tap the media icon, select up to 20 photos or videos in the order you want them, write up to 500 characters, tap Post. Meta's limits: JPEG or PNG, 8 MB per image, 320–1440 px wide; the first item's aspect ratio is applied to the whole set. Export every slide at the same size — 1080×1350 (4:5) or 1080×1080 — and the same files work on Instagram unchanged.
What a Threads carousel is
A Threads carousel is any post with two or more media items attached: readers swipe through them horizontally inside the feed, the same way an Instagram carousel post works. Meta's Threads documentation caps a carousel at 20 items, which can be images, videos, or both in one set. That cap doubled in September 2024, when the official @threads account announced the move from 10 to 20 — most guides still ranking for this question quote the old number.
Unlike a LinkedIn carousel, there is no separate document format and no PDF: you attach image files directly. Unlike TikTok, there is no music layer. It is the plainest carousel implementation of the major platforms, which also makes it the easiest to post to from any tool that exports PNGs.
Threads carousel size and limits
These are the limits Meta publishes for Threads media in its developer documentation — the only spec Meta puts in writing. They describe API publishing; the app composer isn't documented separately, though the 20-item cap is confirmed for it by Meta's own announcement. Treat the rest as the safe envelope to export inside, not as a promise of what the picker will reject:
Two numbers matter more than the rest. The 1440 px width ceiling means a 1080-wide export is comfortably inside spec, and the standard 1080×1350 slide you would make for Instagram uploads as-is. The 10:1 ratio limit is generous enough to be irrelevant for slides, so the practical rule is simply consistency: Threads displays every item in a carousel at the ratio of the first one, so a set that mixes 4:5 and 1:1 slides ends up with letterboxing or cropping from slide two onward.
How to post a carousel on Threads
The composer is the same on iOS and Android; the desktop site works too, but the app is where most people post.
1. Open Threads and tap +
Tap the + (new thread) button in the bottom bar. A blank composer opens with your profile at the top.
2. Tap the media icon and select your slides
Tap the photo/media icon under the text field and choose from your library. Tap the items in the order you want them to appear — the selection order is the slide order. Up to 20.
3. Check the order and the first slide
The selected media appear as thumbnails in the composer. If one is out of place, tap the × on it and re-select in the right order — the picker order is the only ordering control you can count on across app versions. Make sure the first item is the hook slide — it sets the aspect ratio for the whole carousel and it is the only one people see before deciding to swipe.
4. Write the text
Up to 500 characters. There is no title field, no fold, no "…see more" to design around: the first line is the hook. Keep the text short and let the slides carry the argument.
5. Post
Tap Post. The carousel appears in the feed with the first slide showing and a dot indicator for the rest.
Designing slides that hold up on Threads
Threads is a text-first feed, which changes how a carousel reads compared with Instagram:
- Pick one ratio and stick to it. 4:5 (1080×1350) takes the most vertical space on phones; 1:1 (1080×1080) is the safest if the same slides also go to X or a LinkedIn photo post. Never mix the two in one set.
- Make the type bigger than feels natural. Carousels on Threads sit between short text posts, and readers are in scanning mode. A headline that is comfortable on Instagram is slightly small here.
- Design slide one as a standalone post. On Threads the first slide competes with plain text posts for attention, and there is no caption fold to lean on. If slide one only makes sense after reading the text, it will not earn the swipe.
- Skip the sound-on tricks. There is no auto-added music and no audio layer for image carousels, so any "turn your sound on" slide design copied from TikTok is dead weight.
- Export clean PNGs at exactly 1080 wide. Threads re-compresses uploads like every platform. The Instagram carousel size guide covers the double-compression trap; the fix is the same here — start from a lossless export.
Threads vs Instagram vs X
The same slide files work on all three, but the packaging differs:
- Instagram: also 20 items per carousel, 4:5 recommended, plus music, captions with a fold, and a much larger discovery surface. Design for Instagram first and Threads gets the same set for free.
- Threads: 20 items, no music, 500-character text, first-item ratio rule. Lowest friction of the three.
- X: no swipeable carousel in the standard composer at all — four photos become a grid, and real carousels need the advertiser tools. If you cross-post, the carousel on X is the one that needs rework, not Threads.
If you are still deciding whether the format is worth your time at all, the mechanics of why swiping earns reach are the same everywhere — our explainer on what a carousel post is covers that once so this post doesn't have to.
Design once, post anywhere
The manual path: design each slide at 1080×1350, keep every slide the same ratio, export lossless PNGs, open Threads, attach them in order, write two lines, post. Nothing above is hard; the time goes into the slides themselves.
xcarousel generates a designed carousel from a topic, URL, or PDF and exports pixel-exact PNG slides. There is no Threads preset — Threads isn't a one-click target the way Instagram and LinkedIn are — but the Instagram 4:5 export is already inside every Threads limit above, so the same files upload unchanged. The hour of writing and layout is the part the tool compresses to about a minute; the posting stays yours.