Right now, Instagram posts work best in 1080×1080 px for square, 1080×1350 px for portrait, and 1080×566 px for landscape. That way your pics look sharp and don’t get cropped weird.
Instagram now supports a 3:4 aspect ratio for photos, allowing images to display exactly as taken without automatic cropping. This update applies to both single-photo uploads and carousels, providing a more accurate representation of user content