One panorama, one swipeable post.

Carousels do something feed posts can't: hold a viewer in a single post for longer than three seconds. Instagram's ranking notices that time-on-post and tends to push the post further. So even when you're really posting one image, splitting it into a carousel can buy you a little more reach because the swipe gesture forces a second beat of attention.

The other reason is craft. A horizontal composition — a landscape, a stretched-out illustration, a long quote — usually loses a lot of its impact when it's shrunk into a square thumbnail. Spread across three or five slides, the same composition keeps the left-to-right reading order it was designed with and shows up full-size on a phone.

Instagram serves carousel slides at up to 1080 pixels wide. So if you want a three-slide carousel where each slide is pin-sharp, the source image wants to be at least 3,240 pixels across (3 × 1080). For five slides it's 5,400. For ten — yes, ten is a lot — you're looking at 10,800 pixels.

The tool also clamps height. Instagram caps carousel slides at a 1:1 aspect ratio on the feed (it'll show 4:5 if you push it, but the "grid of slides" aesthetic only works at 1:1). So we take the full width you give us and divide it into evenly-sized square frames, ignoring any extra height above and below. If your source image is wider than the ideal ratio, we center-crop the width. If it's shorter than the ideal ratio, we crop the height. Either way the output is square slides that line up.

Don't put critical detail right at the slice line. The cut falls dead-center between slides, and on most phones the edge of one slide is a real visible gap when someone's mid-swipe. Faces, important type, and logos all want to live a comfortable padding away from those cut points.

Use the first slide to do the work. Most viewers will see only slide one before deciding whether to swipe. Treat it like a thumbnail: it has to make sense on its own, and it has to suggest there's more.

Run a sanity check on a real phone before you post. The desktop preview is fine for spotting alignment errors, but the proportions on a phone screen are different enough that a composition can read beautifully in the editor and underwhelm on the actual feed.

If you want the image to live inside a single post that people swipe — what you're reading about here — this is the right tool.

If you want the image to take over your profile page so visitors see one big composition as the top of your grid, you want the Grid Maker instead — that one cuts a square photo into nine 1:1 tiles you post as separate posts in a specific order.