Instagram carousel size, settled

Landscape exists. Ignore it. It takes the least height of any option, which on a phone means the least attention.

A phone screen is tall. A 4:5 slide occupies roughly a third more of it than a square does, and the extra height arrives at the exact moment someone decides whether to keep swiping. You are not choosing a shape, you are choosing how much of the screen you get to hold.

Whatever you pick, pick it once. A carousel that changes shape between slides makes the feed jump as people swipe, and the jump is what stops them.

It re-encodes everything. That is not negotiable, so the only thing you control is the quality of what you hand over. Instagram keeps up to 1440 pixels of width and scales anything larger down; below that it scales up, which is why a 1080-wide export can look soft on a recent phone even though the number sounds right.

Export at 1440 across, in the shape you chose, and let their compression work from a clean source. Nothing else you do at upload time matters nearly as much.

Instagram allows twenty. Use three to seven. Three is enough to establish that something continues across the cuts, and past seven the drop-off does the editing for you.

One exception: a single wide photograph sliced across every slide can carry more, because each swipe reveals a piece of something the viewer already wants to finish. The tool caps at 10 for that reason.

Dimensions alone will not make a post read as one thing. That comes from composing across the full width rather than slide by slide, which is the method here.