Aspect Ratio
Aspect ratio is the proportional relationship between an image or video's width and height, written as width:height — like 16:9, 9:16, or 1:1.
Formula
Aspect ratio = Width : Height (e.g. 1920 × 1080 = 16:9)
Aspect ratio defines an asset's shape independent of its pixel size. 16:9 is standard widescreen (YouTube, TVs); 9:16 is vertical for Reels, TikTok, and Stories; 1:1 is square; 4:5 is the tall portrait that performs best in the Instagram feed.
To resize without distorting, keep the ratio constant — scale width and height by the same factor. Publishing in the wrong ratio for a platform means letterbox bars or cropped-off edges, so match the ratio to where the content will live.