The proportional relationship of a video or image’s width to its height, expressed as W:H (e.g. 9:16, 1:1, 16:9).
Aspect ratio determines how an image or video fits inside a platform's feed slot. The four ratios that matter for content creators: 9:16 (vertical, Reels/Shorts/TikTok/Stories), 1:1 (square, Instagram feed legacy), 4:5 (portrait, Instagram feed current), 16:9 (horizontal, YouTube/desktop).
Each platform has a preferred ratio and a tolerated set. Instagram feed accepts 1:1, 4:5, and 16:9 — but 4:5 occupies the most pixels in the feed and gets the most engagement per impression. Instagram Reels demands 9:16. LinkedIn accepts 16:9 video and 1:1 image but renders 1:1 largest on mobile.
Mismatched aspect ratios get letterboxed (black bars) or auto-cropped (subject offscreen). Either signals "lazy cross-post" to the algorithm and to viewers. Kompozy renders each output at the destination platform's native ratio per the persona's outlet config.