A square crop is the safest shape for social media. It looks tidy in a feed, works for profile pictures and keeps your subject in focus. Here is how to crop a photo to a perfect 1:1 square for free and prepare it for Instagram.
Why square?
A 1:1 image displays the same way almost everywhere, so you do not have to worry about edges being cut off. Instagram also supports portrait and landscape posts, so square is not the only option, but it is a dependable default.