Aspect Ratio Calculator

Calculate dimensions that keep the same aspect ratio. Free online tool for images, video, and screens. No signup, instant results.

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Frequently asked questions

What is a common aspect ratio?
16:9 (widescreen HD), 4:3 (classic TV), 21:9 (ultrawide cinema), 1:1 (Instagram square), 9:16 (vertical portrait/reels).
How does the tool simplify the ratio?
It divides both width and height by their greatest common divisor (GCD). 1920×1080 → GCD 120 → 16:9.
Why does my image look stretched?
The new dimensions no longer match the original ratio. Enter the original width and height, then a new width, and the tool fills in the height that keeps the proportions. It only calculates in that direction.
What is aspect ratio in videos?
The width-to-height ratio of the frame. 16:9 is YouTube default. 9:16 is vertical mobile (TikTok, Instagram Reels). 4:5 is Instagram feed.
Why is my simplified ratio something like 683:384?
The tool divides both sides by their greatest common divisor without snapping to a nearby standard. A 1366x768 laptop screen genuinely is not 16:9, which is why the result looks unusual.
Is the calculated height rounded?
Yes, to the nearest whole pixel. On small targets that rounding shifts the real ratio by a fraction of a percent, which is normally invisible but can matter for tiling.