You have taken the most amazing image and you have posted it on Instagram and you are expecting to see lots of likes and comments for your efforts, and you don’t get as many as you were hoping!
One of the reasons might be the size and shape of your post, and you have to check if it is formatted to be presented at its best on Instagram.
Instagram offers a range of photo size formats, Landscape, Square or Portrait are the most popular, though panoramic and other formats may also be used, though which is the best for Instagram and which one will get you the most engagement?

The composition of your image does have a big factor on the picture you post, with most landscape images working best for a wider format and most portrait shots naturally being ideal for an upright picture format.
Instagram Post Size
Landscape Posts (16:9)
Instagram recommends a post ratio of 1.91:1, but you are happily able to use a ratio of 16:9 for your landscape images.
I also post my landscape images with a minimum height of 1080px and 1350px wide, which isn’t a classic landscape ratio though works out at 5:4 and opposite to Instagram’s recommended 4:5, and by making the size of the picture a minimum 1080px Instagram doesn’t compress it too much..
Square Posts (1:1)
Square images are a really useful halfway house, especially as Instagram crops your portrait or landscape image when displaying it on the profile grid. Once again it is always best to use a minimum result ion of 1080px for the shortest side, which with a square image is all the sides.
Portrait Posts (4:5)
Portrait images must have an aspect ratio of 4:5, and any other ratio will be cropped by Instagram when it is posted.
Vertical posts take up the most space on the screen and appear bigger to your viewer and are the most optimised format for Instagram. Although these take up the more real estate on the feed they will be gropped when shown on your grid and sonderation my be given when posting this format, if you want to have a consistent looking profile grid.
I recommend using a 4:5 format, with a minimum of 1080px on the shortest size. This will give your picture the most bang when your viewers see it and make them more inclined to dwell on the image and like it.
I usually post my images as 2160px/2700px.
Below are a couple of examples of a landscape post and a portrait post:
- Landscape

When using landscape or wide images you only use up half the screen and your picture has to be presented smaller for it to fit on the screen.
- Portrait

With portrait the whole of the screen is used up, so much so that there is very little room on the screen for a description or any other detail other the than the image.
Conclusion
My suggestion and what I always try to do is post in Portrait, upright format, 4:5, 4 wide and 5 high, and using this format shows off as much as your image as possible. I also try to take my pictures in this format, even if they are a landscape, with posting to Instagram in mind. I accept that sometimes for the sake of the image having it in landscape would work best, though even then if you can post as a square image that would be more desirable.