Instagram Image Sizes and Aspect Ratios: The Complete Spec
Every Instagram image and video dimension in one table, plus what actually happens to files that fall outside the feed's accepted aspect ratio window.
Instagram guides
Plain-English guides on engagement, sizing, captions and growth — written to be checked, not believed. Every claim that can be verified links to where it came from, and every number you can work out yourself has a free browser-based tool attached.