Ratios, slide counts, and the rule that crops a whole set without telling you.
Five figures that decide whether a carousel posts the way you drew it.
| Ratio | Pixels | Aspect | Use it when |
|---|---|---|---|
| Portrait | 1080 × 1350 | 4:5 | Instagram-first, and what Instagram itself recommends. The default unless you have a reason. |
| Square | 1080 × 1080 | 1:1 | Cross-posting, anything that also goes to LinkedIn. Loses the most in the profile grid. |
| Grid-safe | 1080 × 1440 | 3:4 | Nothing is cropped in the profile grid. Use it when the artwork runs to the edges. |
| Vertical | 1080 × 1920 | 9:16 | Stories, Reels covers, TikTok, Shorts — not feed carousels. |
The first slide decides the crop. Instagram applies the aspect ratio of slide one to the whole carousel, so a square cover in front of a 4:5 set silently trims every slide behind it.
And 4:5 is worth the trouble: it takes about a quarter more feed height than a square, for the same scroll. Export the set at one ratio, and check the cover is that ratio too.
Instagram raised the limit from ten to twenty in 2024, and the number that matters is neither. A carousel is read like a stack of cards: the cover earns the first swipe, the second decides whether there is a third, and the drop-off after that is steep whatever the cap says.
Write the number of slides the idea needs — usually a cover, three to five points and a close — and stop. The floor is two, because one image is not a carousel.
Instagram crops the whole set to the aspect ratio of the first slide. One square cover in front of a 4:5 set quietly trims the top and bottom off every slide behind it.
Feed carousels are not covered by app chrome, but they are shown small. Keep at least 60px of margin and a headline that survives being a thumbnail on a phone.
“5 tips for X” on a plain background is a table of contents. The cover is the only slide most people see, so it has to carry the claim, not announce it.
Up to 20, raised from 10 in 2024. Two is the minimum. More slides is not better: the useful number is however many the idea needs, because the drop-off after slide three is steep whatever the cap says.
4:5 (1080×1350) takes roughly 25% more height in a mobile feed than a square, for the same scroll. Square is the safer default if the same set also goes to LinkedIn or X, where a tall image gets cropped in preview.
Yes — and this is the one that catches people. Instagram crops the entire carousel to the aspect ratio of the FIRST slide. One square slide at the front and the rest of your 4:5 set loses its top and bottom.
As a document post — a PDF rather than a set of images — with each page at 1:1 or 4:5. PostPop exports the slides; you assemble them into the PDF LinkedIn wants.
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