The three shapes
Square is 1:1 and the historical default. Portrait is 4:5 and is the tallest ratio Instagram permits in the feed, which means it occupies the most vertical space on a phone screen — measurably more attention for the same post. Landscape is 1.91:1 and takes the least.
If you are posting product photography and want reach, portrait is the default worth adopting. Anything taller than 4:5 gets centre-cropped.
Carousels crop to the first image
Every image in a carousel is cropped to the aspect ratio of the first one. This catches people out constantly: a carousel that mixes a portrait shot with square ones has the squares cropped, usually straight through the product.
Size every image in a carousel identically before uploading. This is exactly the kind of tedious batch job this tool exists for.
Instagram will recompress whatever you send
There is no way to avoid Instagram’s own compression. What you can control is what it starts from — a clean, correctly sized image at the right dimensions gives the recompression less to do and survives it better than an oversized file that gets downscaled and re-encoded in one step.
This is why "upload the largest file possible" is bad advice for Instagram specifically, even though it is reasonable advice for a marketplace.
Product photos for the grid
One thing worth knowing: your profile grid crops posts to square regardless of what shape they were posted in. If you post 4:5 portrait, keep important detail away from the top and bottom of the frame so the grid thumbnail still makes sense.
Common questions
What is the best Instagram post size?
1080 × 1350 (4:5 portrait) takes the most vertical space in the feed and is the best default for reach. 1080 × 1080 square is the safe alternative, and 1080 × 566 is landscape.
Should I upload images larger than 1080 px?
There is no benefit. Instagram renders feed images at 1080 px wide, so anything larger is downscaled and recompressed. Starting at the target size gives the compression less to do.
Why are my carousel images cropped?
Every image in a carousel is cropped to the aspect ratio of the first image. Resize all of them to the same dimensions before uploading.
Why do my photos look different in my profile grid?
The grid crops every post to square regardless of the shape it was posted in. If you post 4:5 portrait, keep key detail away from the top and bottom edges.