Find the aspect ratio of any width and height, then resize to a new size while keeping the exact proportions — no stretching, no guesswork.
An aspect ratio calculator tells you the proportional relationship between a width and a height — written as width:height, like 16:9 for widescreen video or 1:1 for a square Instagram post. This tool does two jobs: it simplifies any width and height into a clean ratio, and it resizes a picture or video to a new dimension while keeping the proportions locked, so nothing gets stretched or squashed.
Enter the original width and height (or pick a preset like 16:9, 4:3 or 9:16). Then type only the new width and the correct new height is filled in automatically — or type the new height to get the width. The formula is new height = new width × original height ÷ original width. This is exactly how you scale a design, a thumbnail, a banner or a video export without distortion.
16:9 — YouTube, TVs, most video. 9:16 — Reels, TikTok, Stories (vertical). 1:1 — square social posts. 4:3 — older screens and many photos. 3:2 — DSLR photography. 21:9 — ultrawide and cinematic. Match your export to the platform to avoid black bars or awkward cropping.
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